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Eyes with the corneal ectasia keratoconus have performed better than expected (e.g. visual acuity) given their elevated levels of higher-order aberrations that cause rotationally asymmetric retinal blur. Adapted neural processing has been suggested as an explanation but has not been measured across multiple meridional orientations. Using a custom Maxwellian-view laser interferometer to bypass ocular optics, sinusoidal grating neural contrast sensitivity was measured in six eyes (three subjects) with keratoconus and four typical eyes (two subjects) at six spatial frequencies and eight orientations using a two-interval forced-choice paradigm. Total measurement duration was 24 to 28 hours per subject. Neural contrast sensitivity functions of typical eyes agreed with literature and generally showed the oblique effect on a linear-scale and rotational symmetry on a log-scale (rotational symmetry was quantified as the ratio of the minor and major radii of an ellipse fit to all orientations within each spatial frequency; typical eye mean 0.93, median 0.93; where a circle = 1). Mean sensitivities of eyes with keratoconus were 20% to 60% lower (at lower and higher spatial frequencies respectively) than typical eyes. Orientation-specific neural contrast sensitivity functions in keratoconus showed substantial rotational asymmetry (ellipse radii ratio: mean 0.84; median 0.86) and large meridional reductions. The visual image quality metric VSX was used with a permutation test to combine the asymmetric optical aberrations of the eyes with keratoconus and their measured asymmetric neural functions, which illustrated how the neural sensitivities generally mitigated the detrimental effects of the optics.

Visual redundancy detection is essential for image and video communication. Human visual system (HVS) is difficult to perceive the pixel magnitude change below a certain visibility threshold which is also known as just-noticeable-difference (JND). In this letter, we present an efficient JND estimation approach for screen content images by considering high-frequency sensitivity and orientation sensitivity correction. Specifically, to better quantify the visual redundancy, we investigate the visibility threshold based on the high-frequency distortion sensitivity. To obtain the orientation sensitivity correction, we divide the screen image pixels into three levels based on the oblique effect that considers the sensitive integrity of edges. Compared with several state-of-the-art JNDs, experimental results show that our method tolerates more perceptual redundancy, and delivers better visual quality under the same injected-noise energy. The implementation of the proposed method is publicly available at https://sites.google.com/site/wangmiaohui/ .

Orientation tuning is a fundamental response property of V1 neurons and has been extensively studied with single-/multiunit recording and intrinsic signal optical imaging. Long-term 2-photon calcium imaging allows simultaneous recording of hundreds of neurons at single neuron resolution over an extended time in awake macaques, which may help elucidate V1 orientation tuning properties in greater detail. We used this new technology to study the microstructures of orientation functional maps, as well as population tuning properties, in V1 superficial layers of 5 awake macaques. Cellular orientation maps displayed horizontal and vertical clustering of neurons according to orientation preferences, but not tuning bandwidths, as well as less frequent pinwheels than previous estimates. The orientation tuning bandwidths were narrower than previous layer-specific single-unit estimates, suggesting more precise orientation selectivity. Moreover, neurons tuned to cardinal and oblique orientations did not differ in quantities and bandwidths, likely indicating minimal V1 representation of the oblique effect. Our experimental design also permitted rough estimates of length tuning. The results revealed significantly more end-stopped cells at a more superficial 150 μm depth (vs. 300 μm), but unchanged orientation tuning bandwidth with different length tuning. These results will help construct more precise models of V1 orientation processing.

Visual perception depends fundamentally on statistical regularities in the environment to make sense of the world. One such regularity is the orientation anisotropy typical of natural scenes; most natural scenes contain slightly more canonical (horizontal and vertical) information than oblique information. This property is likely a primary cause of the oblique effect in which subjects experience greater perceptual fluency with horizontally and vertically oriented content than oblique. Recent changes in the visual environment, including the “carpentered” content in urban scenes and the framed, caricatured content in digital screen media presentations, may have altered the typical (natural) level of orientation anisotropy. The current work evaluated whether digital visual experience, or visual experience with framed digital content, has the potential to alter the magnitude of the oblique effect in visual perception. Experiment 1 successfully established a novel eye-tracking method capable of indexing the visual oblique effect quickly and reliably and demonstrated the oblique effect. Experiment 2 used this method and found that one session of exposure to a specific video game altered visual orientation perception. Taken together, these results indicate that exposure to the realistic, but caricatured scene statistics of digital screen media, can alter visual contour perception in one session.

This study aimed to explore whether there was an effect on steady-state visual evoked potential (SSVEP) visual acuity assessment from the oblique effect or the stimulus orientation. SSVEPs were induced by seven visual stimuli, e.g., the reversal sinusoidal gratings with horizontal, two oblique, and vertical orientations, reversal checkerboards with vertical and oblique orientations, and oscillating expansion-contraction concentric-rings, at six spatial frequency steps. Ten subjects participated in the experiment. Subsequently, a threshold estimation criterion was used to determine the objective SSVEP visual acuity corresponding to each visual stimulus. Taking the SSVEP amplitude and signal-to-noise-ratio (SNR) of the fundamental reversal frequency as signal characteristics, both the SSVEP amplitude and SNR induced by the reversal sinusoidal gratings at 3.0 cpd among four stimulus orientations had no significant difference, and the same finding was also shown in the checkerboards between vertical and oblique orientation. In addition, the SSVEP visual acuity obtained by the threshold estimation criterion for all seven visual stimuli showed no significant difference. This study demonstrated that the SSVEPs induced by all these seven visual stimuli had a similarly good performance in evaluating visual acuity, and the oblique effect or the stimulus orientation had little effect on SSVEP response as well as the SSVEP visual acuity.

Few studies have examined the stability of the representation of the position of sound sources in spatial working memory. The goal of this study was to verify whether the memory of sound position declines as maintenance time increases. In two experiments, we tested the influence of the delay between stimulus and response in a sound localization task. In Experiment 1, blindfolded participants listened to bursts of white noise originating from 16 loudspeakers equally spaced in a 360-degree circular space around the listener in such a way that the nose was aligned to the zero-degree coordinate. Their task was to indicate sounds' position using a digital pointer when prompted at varying delays: 0, 3, and 6 s after stimulus offset. In Experiment 2, the task was analogous to Exp. 1 with stimulus-response delays of 0 or 10 s. Results of the two experiments show that increasing stimulus-response delays up to 10 s do not impair sound localization. Participants systematically overestimated the eccentricity of the auditory stimulus by shifting their responses either toward the 90-degree coordinate, in alignment with the right ear, or toward the 270-degree coordinate, in alignment with the left ear. Such bias was analogous in the front and in the rear azimuthal space and was only marginally influenced by the delay conditions. We conclude that the representation of auditory space in working memory is stable, but directionally biased with systematic overestimation of eccentricity.

The Oppel–Kundt illusion consists in the overestimation of the length of filled versus empty extents. Two experiments explored its relation to the horizontal-vertical illusion, which consists in the overestimation of the length of vertical versus horizontal extents, and to the oblique effect, which consists in poorer discriminative sensitivity for obliquely as opposed to horizontally or vertically oriented stimuli. For Experiment 1, Kundt’s (1863) original stimulus was rotated in steps of 45° full circle around 360°. For Experiment 2, one part of the stimulus remained at a horizontal or vertical orientation, whereas the other part was tilted 45° or 90°. The Oppel–Kundt illusion was at its maximum at a horizontal orientation of the stimulus. The illusion was strongly attenuated with L-type figures when the vertical part was empty, but not enhanced when this part was filled, suggesting that the horizontal-vertical illusion only acts on nontextured extents. There was no oblique effect.

Contains fulltext : 240011.pdf (Publisher’s version ) (Open Access) Although confidence is commonly believed to be an essential element in decision-making, it remains unclear what gives rise to one's sense of confidence. Recent Bayesian theories propose that confidence is computed, in part, from the degree of uncertainty in sensory evidence. Alternatively, observers can use physical properties of the stimulus as a heuristic to confidence. In the current study, we developed ideal observer models for either hypothesis and compared their predictions against human data obtained from psychophysical experiments. Participants reported the orientation of a stimulus, and their confidence in this estimate, under varying levels of internal and external noise. As predicted by the Bayesian model, we found a consistent link between confidence and behavioral variability for a given stimulus orientation. Confidence was higher when orientation estimates were more precise, for both internal and external sources of noise. However, we observed the inverse pattern when comparing between stimulus orientations: although observers gave more precise orientation estimates for cardinal orientations (a phenomenon known as the oblique effect), they were more confident about oblique orientations. We show that these results are well explained by a strategy to confidence that is based on the perceived amount of noise in the stimulus. Altogether, our results suggest that confidence is not always computed from the degree of uncertainty in one's perceptual evidence but can instead be based on visual cues that function as simple Heuristics to confidence. 19 p.

Although confidence is commonly believed to be an essential element in decision making, it remains unclear what gives rise to one’s sense of confidence. Recent Bayesian theories propose that confidence is computed, in part, from the degree of uncertainty in sensory evidence. Alternatively, observers can use physical properties of the stimulus as a heuristic to confidence. In the current study, we developed ideal observer models for either hypothesis and compared their predictions against human data obtained from psychophysical experiments. Participants reported the orientation of a stimulus, and their confidence in this estimate, under varying levels of internal and external noise. As predicted by the Bayesian model, we found a consistent link between confidence and behavioral variability for a given stimulus orientation. Confidence was higher when orientation estimates were more precise, for both internal and external sources of noise. However, we observed the inverse pattern when comparing between stimulus orientations: although observers gave more precise orientation estimates for cardinal orientations (a phenomenon known as the oblique effect), they were more confident about oblique orientations. We show that these results are well explained by a strategy to confidence that is based on the perceived amount of noise in the stimulus. Altogether, our results suggest that confidence is not always computed from the degree of uncertainty in one’s perceptual evidence, but can instead be based on visual cues that function as simple heuristics to confidence.

BACKGROUND AND OBJECTIVE: The Oblique Effect denotes superior performance for perceiving horizontal or vertical rather than diagonal or oblique stimuli (Appelle, 1972). The current research investigated the Oblique Effect in patients with mild cognitive impairment (MCI). RESEARCH DESIGN AND METHODS: Four statistically-determined groups were studied; patients with little to no cognitive impairment (non-MCI); subtle cognitive impairment (SCI); amnestic MCI (aMCI); and a combined mixed/dysexecutive MCI (mixed/dys MCI). The Oblique Effect was measured with the Judgment of Line Orientation Test (JOLO). Comprehensive neuropsychological assessment was also obtained. Between-group differences for JOLO oblique and non-oblique test stimuli were analyzed. Hierarchical linear regression models were constructed to identify relations between accuracy for oblique and non-oblique test items and neurocognitive domains. RESULTS: The mixed/dys MCI group demonstrated lower accuracy for oblique test items compared to non-MCI patients. Accurate responding to oblique test items was associated with better performance on tests measuring executive control, processing speed, naming/lexical retrieval, and verbal concept formation. No between-group differences were seen for non-oblique items and these items were not associated with cognition. DISCUSSION AND IMPLICATIONS: Significant impairment on oblique test items distinguished patients with multi-domain/dysexecutive MCI from non-MCI patients. Accurate responding to oblique test items was associated with a complex array of neuropsychological tests suggesting that multidimensional neuropsychological skills underlie the visuospatial reasoning abilities necessary for successful oblique line identification. Research associating the Oblique Effect with additional test paradigms and MRI-defined neuroanatomical regions in MCI may provide more information about the brain-behavior relations that underlie MCI subtypes.

People perceive better in cardinal directions compared with oblique ones. This directional effect, called oblique effect, has been documented in perception studies for a long time. However, typical motor studies do not differentiate learning in different directions. In this study we identify a significant directional effect in motor learning using visuomotor rotation paradigms. We find that adaptation to visual perturbations yields more savings when both initial learning and relearning are performed in cardinal directions than in oblique directions. We hypothesize that this directional effect arises from relatively higher error saliency in cardinal directions. Consistent with this hypothesis, we successfully increased savings in the oblique directions, which showed no saving effect before, by enhancing the error saliency with augmented visual feedback during learning. Our findings suggest that movement direction plays an important role in motor learning, especially when learning signals are direction specific. Our results also provide new insights about the role of motor errors in the formation and retrieval of motor memory and practical implications for promoting learning in motor rehabilitation and athletic training. NEW & NOTEWORTHY People perceive better when the stimulus is in cardinal directions than in oblique directions. Whether a similar directional effect exists in motor learning is unknown. Using a motor learning paradigm, we show that people relearn to compensate for a previously encountered perturbation faster when they move in cardinal directions than when they move in oblique directions. Further experimentation supports that this motor directional effect likely results from better sensory saliency of motor errors in cardinal directions.

A common set of tasks frequently employed in the neuropsychological assessment of patients with visuomotor or perceptual deficits are the card-posting and the perceptual orientation matching tasks. In the posting task, patients have to post a card (or their hand) through a slot of varying orientations while the matching task requires them to indicate the slot's orientation as accurately as possible. Observations that damage to different areas of the brain (dorsal vs. ventral stream) is associated with selective impairment in one of the tasks - but not the other - has led to the suggestion that different cortical pathways process visual orientation information for perception versus action. In three experiments, we show that this conclusion may be premature as posting does not seem to rely on the processing of visual orientation information but is instead performed using obstacle avoidance strategies that require an accurate judgement of egocentric distances between the card's and the slot's edges. Specifically, we found that while matching is susceptible to the oblique effect (i.e., common perceptual orientation bias with higher accuracy for cardinal than oblique orientations), this was not the case for posting, neither in immediate nor in memory-guided conditions. In contrast to matching, posting errors primarily depended on biomechanical demands and reflected a preference for performing efficient and comfortable movements. Thus, we suggest that previous dissociations between perceptual and visuomotor performance in letter posting tasks are better explained by impairments in egocentric and allocentric spatial processing than by independent visual processing systems.

Literature on the development of global motion and global form perception demonstrated their asynchronous developmental trajectories. However, former studies have failed to clearly establish the critical period of maturation for these specific abilities. This study aimed to analyze the developmental trajectories of global motion and global form discrimination abilities by controlling for basic visual functions and general cognitive ability and to present the global motion and global form normative scores. A sample of 456 children and adolescents (4–17 years of age) and 76 adults recruited from the Italian and Swedish general population participated in the study. Motion and form perception were evaluated by the motion coherence test and form coherence test, respectively. Raven’s matrices were used to assess general cognitive ability, the Lea Hyvarinen chart test was used for full- and low-contrast visual acuity, and the TNO test was used for stereopsis. General cognitive ability and basic visual functions were strongly related to motion and form perception development. Global motion perception had an accelerated maturation compared with global form perception. For motion perception, an analysis of the oblique effect’s development showed that it is present at 4 years of age. The standardized scores of global motion and form coherence tests can be used for clinical purposes.

Cultural forms are constrained by cognitive biases, and writing is thought to have evolved to fit basic visual preferences, but little is known about the history and mechanisms of that evolution. Cognitive constraints have been documented for the topology of script features, but not for their orientation. Orientation anisotropy in human vision, as revealed by the oblique effect, suggests that cardinal (vertical and horizontal) orientations, being easier to process, should be overrepresented in letters. As this study of 116 scripts shows, the orientation of strokes inside written characters massively favors cardinal directions, and it is organized in such a way as to make letter recognition easier: Cardinal and oblique strokes tend not to mix, and mirror symmetry is anisotropic, favoring vertical over horizontal symmetry. Phylogenetic analyses and recently invented scripts show that cultural evolution over the last three millennia cannot be the sole cause of these effects.

This study addressed the question whether 6-month-olds’ speed discrimination is ratio dependent and whether an oblique effect (i.e., more accurate discrimination of cardinally as opposed to obliquely oriented objects) affects their speed discrimination skills. Infants were habituated to visual displays showing a ball moving with constant speed and tested with the familiar and a novel speed in the test phase. This ball moved either on a cardinally or obliquely oriented trajectory. Irrespective of orientation, infants looked longer at the novel speed when speeds differed by a ratio of 1:2, whereas they looked indiscriminable at the novel and familiar speeds when they differed by a ratio of 2:3. Our results show remarkable parallels to infants’ ratio-dependent discrimination behavior in other domains (time, distance, and number), implying that different magnitudes may be processed by the same underlying mechanism. However, our findings also indicate that speed discrimination was not influenced by spatial orientation in a similar way as has been found for other visual perceptual processes.

Human observers are exquisitely sensitive to curvature deformations along a circular closed contour (Wilkinson, Wilson, & Habak, 1998; Hess, Wang, & Dakin, 1999; Loffler, Wilson, & Wilkinson, 2003). Such remarkable sensitivity has been attributed to the curvature encoding scheme used by V4 neurons, which typically are assumed to be equally sensitive to curvature at all polar angles (Pasupathy & Connor, 2001, 2002; Carlson, Rasquinha, Zhang, & Connor, 2011). To test the assumption that detection thresholds for curvature deformations are invariant across polar angles, we used a novel stimulus class we call Difference of Gaussian (DoG) contours that allowed us to independently manipulate the amplitude, angular frequency, and polar angle of curvature of a closed-contour shape while measuring contour-curvature thresholds. Our results demonstrate that (a) detection thresholds were higher when observers were uncertain about the location of the curvature deformation, but on average, thresholds did not vary significantly across 24 polar angles; (b) the direction and magnitude of the oblique effect varies across individuals; (c) there is a strong association between detecting a contour deformation and identifying its location; (d) curvature detectors may serve as labeled lines.

Analysis of people's preferences concerning the orientation of paintings has revealed robust evidence for what is known as the aesthetic oblique effect. That is, horizontal/vertical lines are preferred, aesthetically-speaking, over oblique lines in painting by both artists and those who view their works. At the same time, however, researchers have also demonstrated the existence of a preference for linear food elements (be they presented on the plate or on product packaging) when shown ascending to the right (rather than the left, or else when presented in any another orientation). Here, we report on three online studies, the first demonstrating that people visually prefer an edible version of one of Kandinsky's paintings when presented horizontally (while preferring either the horizontal or vertical orientation for the painting on which the dish was based; Experiment 1). In a second study, a similar preference for the horizontal/vertical alignment of a much simpler langoustine dish, with a single dominant linear element, was also documented. This preference for the canonical orientations was also reported in a third experiment with another visually-simple chef-prepared dish. Taken together, these results therefore emphasize the similarity in aesthetic preferences for the horizontal/vertical alignment when viewing either paintings or certain chef-prepared plates of food. At the same time, however, these results also raise the question of what factors determine whether the horizontal/vertical or the ascending to the right preference dominates when plating food.

Purpose: We investigated the pattern of meridional anisotropies, if any, for pattern onset-offset visual evoked potential (POVEPs) responses and psychophysical grating acuity (GA) in children with normal letter visual acuity (20/20 or better). \ud \ud Methods: A total of 29 children (aged 3-9 years), nine of whom were astigmatic (AS), were recruited. Orientation-specific monocular POVEPs were recorded in response to sinewave grating stimuli oriented along the subjects' principal AS meridians. Horizontal and vertical gratings were designated Meridians 1 and 2, respectively, for nonastigmatic patients (Non-AS). Binocular POVEPs in response to the same stimuli, but oriented at 45°, 90°, 135°, and 180°, were recorded. Psychophysical GAs were assessed monocularly and binocularly along the same meridians using the same stimuli by a 2-alternative-forced-choice staircase technique. The C3 amplitudes and peak latencies of the POVEP and GAs were compared across meridians using linear mixed models (monocular) and ANOVA (binocular). \ud \ud Results: There were significant meridional anisotropies in monocular C3 amplitudes regardless of astigmatism status (P = 0.001): Meridian 2 (mean ± SE Non-AS, 30.13 ± 2.07 μV; AS, 26.53 ± 2.98 μV) was significantly higher than Meridian 1 (Non-AS, 26.14 ± 1.87 μV; AS, 21.68 ± 2.73 μV; P = 0.019), but no meridional anisotropies were found for GA or C3 latency. Binocular C3 amplitude in response to horizontally oriented stimuli (180°, 29.71 ± 3.06 μV) was significantly lower than the oblique (45°, 36.62 ± 3 .05 μV; P = 0.03 and 135°, 35.95 ± 2.92 μV; P = 0.04) and vertical (90°, 37.82 ± 3.65 μV; P = 0.02) meridians, and binocular C3 latency was significantly shorter in response to vertical than oblique gratings (P ≤ 0.001). \ud \ud Conclusions: Meridional anisotropy was observed in children with normal vision. The findings suggest that horizontal gratings result in a small, but significantly lower POVEP amplitude than for vertical and oblique gratings.

Optical treatment is the primary treatment of all types of amblyopia that has a refractive component. However, it is unclear how optical treatment impacts cortical processing in amblyopic children as some of them may readily improve letter recognition visual acuity (treatment responders) but others may not (treatment non-responders). The main aim was to investigate the electrophysiological and psychophysical effects of optical treatment in children who have been newly-diagnosed with amblyopia in comparison with normal maturation in non-amblyopic children. The secondary aim was to explore whether pattern onset-offset visual evoked potentials (POVEPs) and psychophysical grating acuities (GA) may be predictive of clinically significant improvements in letter recognition visual acuity (VA) after four months of optical treatment. The primary outcome measures were POVEP C3 amplitude and C3 latency and GA which were assessed in response to orientation-specific stimuli. The testing protocol was designed to optimize the assessment of meridional anisotropies and was able to identify children with refractive amblyopia and to monitor treatment outcomes. The study presented evidence that four months of optical treatment improved POVEP C3 amplitude on average, although within the amblyopic group, a subset of refractive amblyopes were not found to significantly improve in letter visual acuity. A comparison control group, comprised of non-amblyopic children, were also monitored over two visits four months apart, which represented age-normal characteristics and maturation. Meridional anisotropies were found to be a potentially useful indicator of normality, as there was evidence that orientation-specific neural mechanisms differed for the responders and non-responders to optical treatment, with the responders showing anisotropies more consistent with the control data. An onset of horizontal effect may indicate that the amblyopic visual systems are improving. Consequently, lower POVEP C3 amplitude in response to horizontally oriented grating stimuli at baseline was found to be a potential predictor of responder status after four months of optical treatment. The findings added new knowledge into the understanding of the electrophysiological and psychophysical effects of optical treatment in refractive amblyopia.

Orientation perception is a fundamental property of the visual system and an important basic processing stage for visual scene perception. Neurophysiological studies have found broader tuning curves and increased noise in orientation-selective neurons of senescent monkeys and cats, results that suggest an age-related decline in orientation perception. However, behavioral studies in humans have found no evidence for such decline, with performance being comparable for younger and older participants in orientation detection and discrimination tasks. Crucially, previous behavioral studies assessed performance for cardinal orientation only, and it is well known that the human visual system prefers cardinal over oblique orientations, a phenomenon called the oblique effect. We hypothesized that age-related changes depend on the orientation tested. In two experiments, we investigated orientation discrimination and reproduction for a large range of cardinal and oblique orientations in younger and older adults. We found substantial age-related decline for oblique but not for cardinal orientations, thus demonstrating that orientation perception selectively declines for oblique orientations. Taken together, our results serve as the missing link between previous neurophysiological and human behavioral studies on orientation perception in healthy aging.

Purpose: We investigated and characterized the patterns of meridional anisotropies in newly diagnosed refractive amblyopes using pattern onset–offset visual evoked potentials (POVEPs) and psychophysical grating acuity (GA).\ud \ud Methods: Twenty-five refractive amblyopes were recruited and compared with non-amblyopic controls from our previous study. Monocular POVEPs were recorded in response to sinewave 4 cycles per degree (cpd) grating stimuli oriented along each individual participants' principal astigmatic meridians, which were approximately horizontal (meridian 1) and vertical (meridian 2). Binocular POVEPs in response to the same stimuli, but oriented at 45°, 90°, 135°, and 180°, were recorded. Psychophysical GAs were assessed along the same meridians using a two-alternative non-forced-choice technique. The C3 amplitudes and peak latencies of the POVEPs and GAs were compared across meridians for both groups (refractive amblyopes and controls) using linear mixed models (monocular) and ANOVA (binocular), and post hoc analysis was conducted to determine if meridional anisotropies in this cohort of amblyopes were related to low (≤1.50 diopters [D]), moderate (1.75–2.75 D) and high (≥3.00 D) astigmatism.\ud \ud Results: In the newly diagnosed refractive amblyopes, there were no significant meridional anisotropies across all outcome measures, but the post hoc analysis demonstrated that C3 amplitude was significantly higher in those with low (P = 0.02) and moderate (P = 0.004) astigmatism compared to those with high astigmatism. Refractive amblyopes had poorer GA and C3 amplitudes compared to controls by approximately two lines on the logMAR chart (monocular: P = 0.013; binocular: P = 0.014) and approximately 6 µV (monocular: P = 0.009; binocular: P = 0.027), respectively.\ud \ud Conclusions: Deleterious effects of high astigmatism was evident in newly diagnosed refractive amblyopes, but the neural deficits do not seem to be orientation-specific for the stimulus parameters investigated.

The oblique effect (OE) describes the visuospatial advantage for identifying stimuli oriented horizontally or vertically rather than diagonally; little is known about brain aging and the OE. We investigated this relationship using the Judgment of Line Orientation (JLO) in 107 older adults (∼age = 67.8 ± 6.6; 51% female) together with neuropsychological tests of executive functioning (EF), attention/information processing (AIP), and neuroimaging. Only JLO lines falling between 36-54° or 126-144° were considered oblique. To quantify the oblique effect, we calculated z-scores for oblique errors (zOblique = #oblique errors/#oblique lines), and similarly, horizontal + vertical line errors (zHV), and a composite measure of oblique relative to HV errors (zOE). Composite z-scores of EF and AIP reflected domains associated with JLO performance. Graph theory analysis integrated T1-derived volumetry and diffusion MRI-derived white matter tractography into connectivity matrices analyzed for select network properties. Participants produced more zOblique than zHV errors (p 0.001). Age was not associated with zOE adjusting for sex, education, and MMSE. Similarly adjusted linear regression models revealed that lower EF was associated with a larger oblique effect (p 0.001). Modular analyses of neural connectivity revealed a differential patterns of network affiliation that varied by high versus low group status determined via median split of zOblique and zHV errors, separately. Older adults exhibit the oblique effect and it is associated with specific cognitive processes and regional brain networks that may facilitate future investigations of visuospatial preference in aging.

In some phenomena of visual perception, the motion direction of visual stimuli can affect perception. In particular, asymmetries between oblique directions and cardinal (horizontal and vertical) directions have been reported and are known as oblique effects (e.g., contrast sensitivity and motion threshold). In this study, we investigated how vection strength depends on motion direction. Participants observed random-dot optical flow in a circular field and rated the perceived vection strength. Dot movement was systematically controlled using the following angles: 0° (up), 30°, 45°, 60°, 90°, 120°, 135°, 150°, and 180° (down). We found that vection strength depended on motion direction and was weaker in the oblique directions than cardinal directions. Thus, the effect of motion direction on vection strength was variable, as seen in the shape of the oblique effect.

The ability to judge speed is a fundamental aspect of visual motion processing. Speed judgments are generally assumed to depend on signals in motion-sensitive, directionally selective, neurons in areas such as V1 and MT. Speed comparisons might therefore be expected to be most accurate when they use information within a common set of directionally tuned neurons. However, there does not appear to be any published evidence on how well speeds can be compared for movements in different directions. We tested speed discrimination judgments between pairs of random-dot stimuli presented side-by-side in a series of four experiments (n = 65). Participants judged which appeared faster of a reference stimulus moving along the cardinal or oblique axis and a comparison stimulus moving either in the same direction or in a different direction. The bias (point of subjective equality) and sensitivity (Weber fraction) were estimated from individual psychometric functions fitted for each condition. There was considerable between-participants variability in psychophysical estimates across conditions. Nonetheless, participants generally made more acute comparisons between stimuli moving in the same direction than those moving in different directions, at least for conditions with an upwards reference (~20% difference in Weber fractions). We also showed evidence for an oblique effect in speed discrimination when comparing stimuli moving in the same direction, and a bias whereby oblique motion tended to be perceived as moving faster than cardinal motion. These results demonstrate interactions between speed and direction processing, thus informing our understanding of how they are represented in the brain.

The representation of visual orientation is more accurate for cardinal orientations compared to oblique, and this anisotropy has been hypothesized to reflect a low-level visual process (visual, "class 1" oblique effect). The reproduction of directional and orientation information also leads to a mean error away from cardinal orientations or directions. This anisotropy has been hypothesized to reflect a high-level cognitive process of space categorization (cognitive, "class 2," oblique effect). This space categorization process would be more prominent when the visual representation of orientation degrades such as in the case of working memory with increasing cognitive load, leading to increasing magnitude of the "class 2" oblique effect, while the "class 1" oblique effect would remain unchanged. Two experiments were performed in which an array of orientation stimuli (1-4 items) was presented and then subjects had to realign a probe stimulus within the previously presented array. In the first experiment, the delay between stimulus presentation and probe varied, while in the second experiment, the stimulus presentation time varied. The variable error was larger for oblique compared to cardinal orientations in both experiments reproducing the visual "class 1" oblique effect. The mean error also reproduced the tendency away from cardinal and toward the oblique orientations in both experiments (cognitive "class 2" oblique effect). The accuracy or the reproduced orientation degraded (increasing variable error) and the cognitive "class 2" oblique effect increased with increasing memory load (number of items) in both experiments and presentation time in the second experiment. In contrast, the visual "class 1" oblique effect was not significantly modulated by any one of these experimental factors. These results confirmed the theoretical predictions for the two anisotropies in visual orientation reproduction and provided support for models proposing the categorization of orientation in visual working memory.

Motion direction discrimination in humans is worse for oblique directions than for the cardinal directions (the oblique effect). For some unknown reason, the human visual system makes systematic errors in the estimation of particular motion directions; a direction displacement near a cardinal axis appears larger than it really is whereas the same displacement near an oblique axis appears to be smaller. Although the perceptual effects are robust and are clearly measurable in smooth pursuit eye movements, all attempts to identify the neural underpinnings for the oblique effect have failed. Here we show that a model of image velocity estimation based on the known properties of neurons in primary visual cortex (V1) and the middle temporal (MT) visual area of the primate brain produces the oblique effect. We also provide an explanation for the unusual asymmetric patterns of inhibition that have been found surrounding MT neurons. These patterns are consistent with a mechanism within the visual system that prevents redundant velocity signals from being passed onto the next motion-integration stage, (dorsal Medial superior temporal, MSTd). We show that model redundancy-reduction mechanisms within the MT-MSTd pathway produce the oblique effect.

Orientation perception is not comparable across all orientations-a phenomenon commonly referred to as the oblique effect. Here, we first assessed the interaction between stimulus contrast and the oblique effect. Specifically, we examined whether the impairment in behavioral performance for oblique versus cardinal orientations is best explained by a contrast or a response gain modulation of the contrast psychometric function. Results revealed a robust oblique effect, whereby asymptotic performance for oblique orientations was substantially lower than for cardinal orientations, which we interpret as the result of multiplicative attenuation of contrast responses for oblique orientations. Next, we assessed how orientation anisotropies interact with attention by measuring psychometric functions for orientations under low or high attentional load. Interestingly, attentional load affects the performance for cardinal and oblique orientations differently: While it multiplicatively attenuates contrast psychometric functions for both cardinal and oblique orientation conditions, the magnitude of this effect is greater for the obliques. Thus, having less attentional resources available seems to impair the response for oblique orientations to a larger degree than for cardinal orientations.

The oblique effect, observed in both humans and animals, refers to the phenomenon of differential perceptual performance in visual recognition tasks that involve horizontal and vertical, vs. diagonal patterns. Furthermore, differences have been found in the visual cortical organization for the horizontal and vertical vs. diagonal representations. However, why such structural differences leading to functional divergence emerge in the first place is yet to be explained. In this paper, we propose a potential explanation for the oblique effect based on the differences in the sampling of oriented edge inputs along different angles due to the mechanics of eye movement. Our hypothesis is that the oblique effect is mainly due to eye movement along the diagonal directions being less precise than the horizontal and the vertical, which causes the sampling of the angles more variable for the diagonal orientations. This will, in turn, lead to structural changes in the visual cortex, which is known to be sensitive to the natural stimulus statistics. We used our Two-Dimensional Linear Homeomorphic Oculomotor Plant Model to simulate saccadic eye movements and sample visual inputs along the eye movement trajectories. Then, we used a multilayer perceptron (as a simple surrogate of the visual cortex) to test how easy it is to learn to classify the different angles from these samples. We found that our results are consistent with the oblique effect data reported in the experimental literature, thus supporting our hypothesis. We expect our work to shed new light on the role of the motor system in determining perceptual organization and function.

This dissertation describes and investigates a debate about differences in the visual system’s anisotropic sensitivity to orientation as well as where and how the brain encodes visual orientation information. Three different visual perceptual patterns are discussed: the Class 1 and 2 oblique effects and the horizontal effect. The oblique effect is the ability to perceive cardinal orientations more easily than oblique orientations, and is found using narrowband stimuli. In the horizontal effect, oblique orientations are perceived most easily, horizontal orientations are perceived worst, and vertical orientations fall in-between, and is found using broadband stimuli. While the majority of authors refer to the oblique effect as a whole, there is a case that it can be divided into Class 1 and Class 2 depending on what the task is measuring: low-level properties of the visual system or higher-level categorization and memory tasks. Moreover, when determining which reference frame the visual system uses to define the oblique effect, there is a disagreement as to whether it is the retinal or gravitational reference frame. To add evidence that there are two classes of the oblique effect and that they are defined by different reference frames (hence the disagreement), retinal, gravitational, and patterncentric coordinates were put in conflict with one another. The effects of phenomenological coordinates were also tested to determine whether top-down cognition played a role in either the Class 1 or Class 2 effect. That the Class 1 oblique effect remained defined by retinal coordinates no matter the test. The Class 2 oblique effect was defined by gravitational coordinates during head tilt with no available patterncentric information. However, when patterncentric coordinates were available the Class 2 effect pattern was defined by these coordinates. Phenomenological coordinates seemed to make no difference to either effect. These results add to current evidence that the oblique effect should be separated into two classes: Class 1, which shows the low-level orientation characteristics of the visual system and is defined by retinal coordinates, and Class 2, which is defined by patterncentric coordinates, and gravitational coordinates when there is no patterncentric input. There have been no studies to date to address the coordinates used by the visual system to define the horizontal effect. The horizontal effect is thought to be important for scene information, so the hypothesis was that it would follow patterncentric coordinates. Again, I tested retinal, gravitational, patterncentric, and phenomenological reference frames. During head tilt (no patterncentric information available), the standard horizontal effect did not remain tied to gravitational coordinates, nor did it transfer completely to retinal coordinates. The pattern did change completely with patterncentric coordinates during scene tilt, indicating that the horizontal effect is important for scene information. However, during scene tilt alone, retinal and…

Human behavior about sliding their fingers on touch screens needs to be understood for the design of radial menus. For this purpose, data about the angles of finger sliding in performing radial pointing to eight predefined directions were collected. The optimal angle ranges and boundaries for these directions were then determined by the proposed mechanism. Consistent with previous research, results showed that the deviations of slide angles for the four diagonal directions were larger than that for the four orthogonal directions. Therefore, to reduce overall pointing errors, the angle ranges for the diagonal directions should be wider than that for the orthogonal directions. Based on the proposed mechanism, the total probability of pointing errors could be limited to 0.05%, compared to the error of 2.00% if the eight angle ranges were evenly divided by the radii of a regular octagon. Besides the angles, the lengths and starting points of the slides were reported and discussed along with the oblique effect, judder effect, and screen orientation. Possible applications of the proposed mechanism for dynamic and personalized radial menus are addressed. Further research would be worthwhile to examine the effects of screen orientation and the number of predefined directions on pointing performances. Moreover, extending the research to mid-air sliding gestures would be of interest and value in designing three-dimensional radial menus. Relevance to industry The proposed mechanism could effectively enhance the accuracy of the selections through radial menus, and could be applied to the remote controls via smart handheld devices.

This study examined the extent to which haptic perception of two-dimensional (2-D) shape is modified by the design of the perceptual task (single-interval categorization vs. two-interval discrimination), the orientation of the angles in space (oblique vs. horizontal), and the exploration strategy (one or two passes over the angle). Subjects (n = 12) explored 2-D angles using the index finger of the outstretched arm. In the categorization task, subjects scanned individual angles, categorizing each as "large" or "small" (2 angles presented in each block of trials; range 80° vs. 100° to 89° vs. 91°; implicit standard 90°). In the discrimination task, a pair of angles was scanned (standard 90°; comparison 91-103°) and subjects identified the larger angle. The threshold for 2-D angle categorization was significantly lower than for 2-D angle discrimination, 4° versus 7.2°. Performance in the categorization task did not vary with either the orientation of the angles (horizontal vs. oblique, 3.9° vs. 4°) or the number of passes over the angle (1 vs. 2 passes, 3.9° vs. 4°). We suggest that the lower threshold with angle categorization likely reflects the reduced cognitive demands of this task. We found no evidence for a haptic oblique effect (higher threshold with oblique angles), likely reflecting the presence of an explicit external frame of reference formed by the intersection of the two bars forming the 2-D angles. Although one-interval haptic categorization is a more sensitive method for assessing 2-D haptic angle perception, perceptual invariances for exploratory strategy and angle orientation were, nevertheless, task-independent.

The details of oriented visual stimuli are better resolved when they are horizontal or vertical rather than oblique. This "oblique effect" has been researched and confirmed in numerous research studies, including behavioral studies and neurophysiological and neuroimaging findings. Although the "oblique effect" has influence in many fields, little research integrated it into computational models. In this paper, we try to explore this inhomogeneity of visual orientation based on Convolutional neural networks (CNNs) in image recognition. We validate that visual orientation inhomogeneity CNNs can achieve comparable performance with higher computational efficiency on various datasets. We can also get the conclusion that, compared with the cardinal information, oblique information is indeed less useful in natural color image recognition. Through the exploration of the proposed model on image recognition, we gain more understanding of the inhomogeneity of visual orientation. It also illuminates a wide range of opportunities for integrating the inhomogeneity of visual orientation with other computational models.

It has long been known that human vision is more sensitive to contours at cardinal (horizontal and vertical) orientations, compared with oblique orientations; this is the “oblique effect.” However, the real-world relevance of the oblique effect is not well understood. Experiments here suggest that this effect is linked to scene perception, via a common bias in the image statistics of scenes. This statistical bias for cardinal orientations is found in many “carpentered environments” such as buildings and indoor scenes, and some natural scenes. In Experiment 1, we confirmed the presence of a perceptual oblique effect in a specific set of scene stimuli. Using those scenes, we found that a well known “scene-selective” visual cortical area (the parahippocampal place area; PPA) showed distinctively higher functional magnetic resonance imaging (fMRI) activity to cardinal versus oblique orientations. This fMRI-based oblique effect was not observed in other cortical areas (including scene-selective areas transverse occipital sulcus and retrosplenial cortex), although all three scene-selective areas showed the expected inversion effect to scenes. Experiments 2 and 3 tested for an analogous selectivity for cardinal orientations using computer-generated arrays of simple squares and line segments, respectively. The results confirmed the preference for cardinal orientations in PPA, thus demonstrating that the oblique effect can also be produced in PPA by simple geometrical images, with statistics similar to those in scenes. Thus, PPA shows distinctive fMRI selectivity for cardinal orientations across a broad range of stimuli, which may reflect a perceptual oblique effect.

The experiments described here used event-related potentials (ERPs) to investigate the neural processes of the horizontal effect, in which visual performance is worst for horizontal and best for oblique orientations. EEGs were recorded while human adult subjects performed an orientation identification task with broad-band noise stimuli. The results showed that the difference between cardinal orientations and oblique orientations first occurred at P2 component around 200ms post-stimulus onset, which is much later than the traditional oblique effect. Additionally, the P3 was much smaller and earlier for oblique orientations than for cardinal orientations. These findings indicated that, compared to the classical oblique effect, the horizontal effect with broad-band noise stimuli might occur at relatively later stages of visual information processing and might involve more complex neural mechanisms.

The current study looked at two theoretical proposals explaining toddlers’ abilities to use cue information for recovering a hidden object that had rolled down a ramp behind an occluded screen. These two approaches, the theory of object directed attention and a landmark-based account, make different predictions regarding the efficacy of an obliquely aligned cue to object position. Accordingly, the search by forty 24-month olds, forty-two 30-month olds, and forty-one 36-month olds for a hidden toy that was cued using either a short versus a long cue, or a vertically aligned versus an obliquely aligned cue, were compared. Analyses of search accuracy revealed that children were more successful when faced with short as opposed to long cues, and when using vertical as opposed to oblique cues. These findings support a landmark-based approach, as opposed to an object-directed attention account, and are discussed with reference to their implications for spatial orientation more generally.

The roles of different afferent systems in the organization of an internal reference frame was studied. The task of visual comparison was performed by subjects under different experimental conditions: in the upright standing position and with the body or head inclined in the frontal plane and with the visual information about an external environment available or not available. It was shown that the dominant orientation of a referent stimulus (the minimum value of the mean error in the reproduction of the stimulus and the minimal variability of the error) was correlated with the body position, mainly the position of the head, more than with the gravitational or visual vertical, even when the visual information was available. This means that the proprioceptive information about the longitudinal axis of body, rather than gravity, is mainly used by the central nervous system for creating the internal representing of vertical during standing.

Orientation discrimination is much better for patterns oriented along the horizontal or vertical (cardinal) axes than for patterns oriented obliquely, but the neural basis for this is not known. Previous animal neurophysiology and human neuroimaging studies have demonstrated only a moderate bias for cardinal versus oblique orientations, with fMRI showing a larger response to cardinals in primary visual cortex (V1) and EEG demonstrating both increased magnitudes and reduced latencies of transient evoked responses. Here, using MEG, we localised and characterised induced gamma and transient evoked responses to stationary circular grating patches of three orientations (0, 45, and 90° from vertical). Surprisingly, we found that the sustained gamma response was larger for oblique, compared to cardinal, stimuli. This "inverse oblique effect" was also observed in the earliest (80 ms) evoked response, whereas later responses (120 ms) showed a trend towards the reverse, "classic", oblique response. Source localisation demonstrated that the sustained gamma and early evoked responses were localised to medial visual cortex, whilst the later evoked responses came from both this early visual area and a source in a more inferolateral extrastriate region. These results suggest that (1) the early evoked and sustained gamma responses manifest the initial tuning of V1 neurons, with the stronger response to oblique stimuli possibly reflecting increased tuning widths for these orientations, and (2) the classic behavioural oblique effect is mediated by an extrastriate cortical area and may also implicate feedback from extrastriate to primary visual cortex.

Neurons in the nervous system make connections with ascending feedforward projections and descending feedback projections, as well as projections from neural structures at the identical hierarchical level. These neurons form extremely complicated neural networks and pathways. Compared with the role of the feedforward projection, much less is known concerning the functional roles of the feedback projection. Visual cortex is a good model for studying functional roles of cortical feedback projections which involve many high functions, such as attention, searching and cognition. The present review mainly focused on the functional roles of feedback projections in the visual system.

Observers consciously prefer Mondrian’s paintings in their original orientation compared with a rotated position—the “oblique effect” (Latto, Brain, & Kelly, 2000). However, this finding’s premise, that all vertical–horizontal orientations of the thick black lines in Mondrian’s oeuvre are preferred, overlooks the fact that the overall balance of these images is also altered when they are reoriented. Thus, balance may regulate the oblique effect, which might influence conscious aesthetic preferences. To address this issue, we explore Hess’s (1965, 1972) claim that observers will unconsciously increase their pupil diameter to pleasing images and constrict it to unpleasant images. We overcame Hess’s methodological limitation of not keeping his images’ luminances and contrast constant across conditions by presenting eight Mondrian paintings (1921–1944) to 30 observers on a CRT for 20 s each in either their original or seven rotated positions. Simultaneously, we measured their pupil size while asking them to report how (dis)pleasing they found each image. We found both evidence for the oblique effect (where image rotation hampers preference) and a correlation between this consciously reported aesthetic preference and unconsciously derived pupil size.

In this study the influence of head-on-body and starting roll position of laser bar and chair was investigated on the perception of, respectively, the visual and postural vertical. Sixty-one subjects, between 21 and 82 years, participated in this study. Results show that head-on-body and starting roll position of laser bar or chair have an influence on the outcome for both subjective visual vertical test (SVV) and subjective postural vertical test (SPV). When head-on-body and starting roll positions are combined the E-effect (deviation of the SVV-SPV opposite to the head-on-body tilt, when the roll tilt of the head is60 degrees -70 degrees ) is observed in the anti-parallel condition, but is suppressed when starting roll position of laser bar or chair are relatively parallel to the length axis of the tilted head. It is suggested that in the assessment of the SVV, when the laser bar is aligned with the length axis of the head (parallel condition), the oblique effect occurs. In the assessment of the SPV, the E-effect is also suppressed in the parallel condition. It is hypothesized that in the parallel conditions, the gravitational reference frames of head and trunk are more aligned with each other providing similar information. In the anti-parallel conditions the reference frames of head and trunk are malaligned, providing contrary input making the estimation of the earth vertical more difficult. It seems that SVV and SPV measurements are influenced by head-on-body and starting roll positions and has to be taken into account in further studies.

We can discriminate departures from the vertical or horizontal more accurately than from other orientations. This may reflect perceptual learning, but the mechanisms behind such learning are not well understood. Here we derive a theory of discrimination learning based on criterion setting theory (CST; Treisman and Williams, 1984), an extension of signal detection theory in which judgment of the current stimulus is partly determined by previous discriminations and context. The CST-based theory of discrimination learning (CST-DL) describes mechanisms which use information from previous acts of discrimination to improve current decision making. CST-DL distinguishes between types of decision criteria and provides an account of anisotropies and context effects affecting discrimination. Predictions from this model are tested in experiments on anisotropies in orientation and depth perception. The results obtained support CST-DL. They also support the conclusion that the account of the retention of sensory information in delayed discrimination provided by CST is superior to the traditional belief that information retention relies on a fixed memory trace or representation of the stimulus.

Stimuli in one modality can affect the appearance and discriminability of stimuli in another, but how they do so is not well understood. Here we propose a theory of the integration of sensory information across modalities. This is based on criterion setting theory (CST; Treisman and Williams, 1984), an extension of signal detection theory which models the setting and adjustment of decision criteria. The theory of sensory integration based on CST (CST-SI) offers an account of cross-modal effects on sensory decision-making; here we consider its application to orientation anisotropy. In this case, CST-SI postulates that the postural senses are concerned with the relations between momentary body posture and the cardinal dimensions of space, vertical and horizontal, and that they also contribute to stabilizing perception of the cardinal orientations in vision through actions on the corresponding visual decision criteria, but that they have little effect on perception of diagonal orientations. Predictions from CST-SI are tested by experimentally separating the contributions that different information sources make to stabilizing the visual criteria. It is shown that reducing relevant kinaesthetic input may increase the variance for discrimination of the visual cardinal axes but not the obliques. Predictions that shift in the location of the psychometric function would be induced by varying the distribution of the test stimuli, and that this effect would be greater for oblique than cardinal axes were confirmed. In addition, peripheral visual stimuli were shown to affect the discrimination of cardinal but not oblique orientations at the focus of vision. These results support the present account of anisotropies.

In previous studies a systematic directional error (the "motor oblique effect") was found in 2D memory pointing movements of healthy adults. In this study we extend these observations to observe that healthy children displayed the same motor oblique effect. In contrast other spatial and temporal movement parameters (mean amplitude error, square directional and amplitude error, latency and the time to maximum velocity) changed with increasing age. Memory delay increased the square directional and amplitude error independent of age. Finally failure of movement inhibition during the delay was more frequent in children compared to adults. These results favor the hypothesis that the motor oblique effect related to perceptual processing biases is constant from childhood while other movement parameters are modulated by age reflecting the continuing optimization of motor control from childhood to adulthood. The dissociation of memory and age effects suggests that motor working memory is already mature in young children.

The oblique effect was first described as enhanced detection and discrimination of cardinal orientations compared with oblique orientations. Such biases in visual processing are believed to originate from a functional adaptation to environmental statistics dominated by cardinal contours. At the neuronal level, the oblique orientation effect corresponds to the numerical overrepresentation and narrower tuning bandwidths of cortical neurons representing the cardinal axes. The anisotropic distribution of orientation preferences over large cortical regions was revealed with optical imaging, providing further evidence for the cortical oblique effect in several mammalian species. Our present study explores whether the dominant representation of cardinal contours persists at different stimulus contrasts. Performing intrinsic optical imaging in the ferret visual cortex and presenting drifting gratings at various orientations and contrasts (100%, 30% and 10%), we found that the overrepresentation of vertical and horizontal contours was invariant across stimulus contrasts. In addition, the responses to cardinal orientations were also more robust and evoked larger modulation depths than responses to oblique orientations. We conclude that orientation maps remain constant across the full range of contrast levels down to detection thresholds. Thus, a stable layout of the functional architecture dedicated to processing oriented edges seems to reflect a fundamental coding strategy of the early visual cortex.

The present research addressed the question of the influence of visual contextual cues on the manual discrimination of spatial orientations in 5-month-old infants. Different types of visual contextual cues were proposed during the haptic discrimination task: congruent-informative, non congruent-informative or noninformative. A familiarization (with a 60-s fixed-duration)/reaction to novelty procedure was used in three experiments. In Experiment 1, a congruent-informative visual context (a visual context composed of alternate black and white stripes tilted to 20 degrees -left) was present and a haptic discrimination between a 20 degrees -left rod and a 30 degrees -left rod was observed (this discrimination was absent without visual context in Gentaz and Streri's study, 2004). In Experiment 2, the visual context cues (composed of black dots) were noninformative, and infants could not discriminate these two oblique rods. In Experiment 3, the presence of a non congruent visual context (a visual context composed of alternate black and white stripes tilted to 20 degrees -left, as in Experiment 1) disturbed the gravitational vertical perception usually observed: infants could not discriminate the vertical rod from the 10 degrees -left rod. These results showed that only the informative (congruent and non congruent) visual contextual cues influenced the haptic discrimination of spatial orientations in 5-month-old infants. These results are discussed in relation with data observed in adults and with the current models of the multisensorial integration and attentional level.

We describe the Drifting Edge Illusion (DEI), in which a stationary edge appears to move when it abuts a drifting grating. Although a single edge is sufficient to perceive DEI, a particularly compelling version of DEI occurs when a drifting grating is viewed through an oriented and stationary aperture. The magnitude of the illusion depends crucially on the orientations of the grating and aperture. Using psychophysics, we describe the relationship between the magnitude of DEI and the relative angle between the grating and aperture. Results are discussed in the context of the roles of occlusion, component-motion, and contour relationships in the interpretation of motion information. In particular, we suggest that the visual system is posed with solving an ambiguity other than the traditionally acknowledged aperture problem of determining the direction of motion of the drifting grating. In this ‘second aperture problem’ or ‘edge problem’, a motion signal may belong to either the occluded or occluding contour. That is, the motion along the contour can arise either because the grating is drifting or because the edge is drifting over a stationary grating. DEI appears to result from a misattribution of motion information generated by the drifting grating to the stationary contours of the aperture, as if the edges are interpreted to travel over the grating, although they are in fact stationary.

The human visual system exhibits lower contrast thresholds for detecting vertical and horizontal gratings compared with those orientated obliquely. This is known as the oblique effect and has been thought to be due wholly to neural factors. In this study, sensitivity to gratings of different orientation is compared when viewing with small and large pupils. Optical aberrations increase with pupil size. In some subjects, we find a statistically significant change in sensitivity to some orientations for the large pupil condition. This suggests that there is an optical component to orientation selectivity induced by the higher-order aberrations of the eye.

In previous studies, we provided evidence for a directional distortion of the endpoints of movements to memorized target locations. This distortion was similar to a perceptual distortion in direction discrimination known as the oblique effect so we named it the "motor oblique effect". In this report we analyzed the directional errors during the evolution of the movement trajectory in memory guided and visually guided pointing movements and compared them with directional errors in a perceptual experiment of arrow pointing. We observed that the motor oblique effect was present in the evolving trajectory of both memory and visually guided reaching movements. In memory guided pointing the motor oblique effect did not disappear during trajectory evolution while in visually guided pointing the motor oblique effect disappeared with decreasing distance from the target and was smaller in magnitude compared to the perceptual oblique effect and the memory motor oblique effect early on after movement initiation. The motor oblique effect in visually guided pointing increased when reaction time was small and disappeared with larger reaction times. The results are best explained using the hypothesis that a low level oblique effect is present for visually guided pointing movements and this effect is corrected by a mechanism that does not depend on visual feedback from the trajectory evolution and might even be completed during movement planning. A second cognitive oblique effect is added in the perceptual estimation of direction and affects the memory guided pointing movements. It is finally argued that the motor oblique effect can be a useful probe for the study of perception-action interaction.

We tested 220 children aged 7-12 yr and 20 university students for visual contrast sensitivity at spatial frequencies of 1.2-21.9 c/deg for vertical, horizontal and oblique sinusoidal gratings. Males had higher mean sensitivity then females and adults had higher mean sensitivity than children. Sensitivity was greater for cardinal than oblique orientations, and this oblique effect increased with spatial frequency and mean sensitivity, and with age in children. Developmental growth of oblique anisotropy can be explained by growth in contrast sensitivity. Different sizes of oblique effect were found between groups living in different locations, but variations were mainly linked to differences in age and contrast sensitivity. Genetic or environmental interpretations of group differences should be treated with caution. Other anisotropies occurred (horizontal was better than vertical and right than left obliques), but these differences were small and irregular and may represent response biases rather than neurological effects.

Despite evidence for the broad direction tuning of global-motion detectors, transparent motion can be detected with comparatively small angular separations. The exact means by which this broad population response is decoded to yield multiple signal directions remains unclear. Consequently, we sought to determine the relationship between angular separation thresholds for transparent motion and the direction-tuning bandwidth of global-motion detectors. Angular separation thresholds were assessed around four axes of motion, with thresholds lower around cardinal axes than the oblique axes. This was also found with lowered signal intensities, despite larger differences between the component directions at threshold, indicating that the transparency oblique effect relies more on the mean direction than the components. Simulations with a model global-motion population suggest this is likely to arise from variation in direction-tuning bandwidths around the cardinal and oblique axes. In a second experiment, adaptation to oblique unidirectional motion produced threshold elevation for a wider range of test directions than adaptation to a cardinal direction. This is consistent with tighter direction tuning around cardinal axes and provides a basis for the transparent-motion oblique effect. Our narrow bandwidth estimates also suggest that transparent-motion detection could rely on bimodal activity within the global-motion stage.