Search

Determining the relief of upcoming terrain is critical to locomotion over rough or uneven ground. Given the significant contribution of stereopsis to perceived surface shape, it should play a crucial role in determining the shape of ground surfaces. The aim of this series of experiments was to evaluate the relative contribution of monocular and binocular depth cues to judgments of ground relief. To accomplish this goal, we simulated a depth discrimination task using naturalistic imagery. Stimuli consisted of a stereoscopically rendered grassy terrain with a central mound or a dip with varying height. We measured thresholds for discrimination of the direction of the depth offset. To determine the relationship between relief discrimination and measures of stereopsis, we used two stereoacuity tasks performed under the same viewing conditions. To assess the impact of ambiguous two-dimensional shading cues on depth judgments in our terrain task, we manipulated the intensity of the shading (low and high). Our results show that observers reliably discriminated ground reliefs as small as 20 cm at a viewing distance of 9.1 m. As the shading was intensified, a large proportion of observers (30%) exhibited a strong convexity bias, even when stereopsis indicated a concave depression. This finding suggests that there are significant individual differences in the reliance on assumptions of surface curvature that must be considered in experimental conditions. In impoverished viewing environments with limiting depth cues, these convexity biases could persist in judgments of ground relief, especially when shading cues are highly salient.

We conducted an empirical investigation of the visual information requirements for target detection and threat identification decisions in the dismounted soldier context. Forty soldiers viewed digital photographs of a person standing against a forested background. The soldiers made two-alternative detection decisions requiring them to determine whether the target was present in the scene, and two-alternative threat identification decisions that required discrimination of the objects held by the target, the clothing worn by the target, and target postures. The images were presented to subjects on a computer display, and variation in the apparent target distance was simulated through digital image magnification and by varying the viewing distance to the display. Image resolution was degraded progressively by spatial frequency filtering and we estimated the resolution threshold in each task. These threshold values were compared with the historical Johnson criteria for predicting imaging device performance. Our data are broadly consistent with the previously reported values, though our threat identification decisions required subjects to perceive information with a larger spatial scale than the Johnson criterion for identification of standing human targets. In a second experiment, we employed a four-alternative identification decision and found results that were consistent with those from Experiment 1. We also confirmed that the spatial scale of visual information used for target acquisition is highly task-specific, and provided a novel demonstration of changes in visual information requirements as a function of target range. These findings pose challenges for models of target acquisition with imaging devices.

This study determined the AC1 agreement values between computer-based color vision tests and the Farnworth–Munsell D-15 (F-D15) and the Holmes–Wright Type A lantern (HWA). The computer-based tests were the United States Air Force Cone Contrast Test (OCCT), Cambridge Color Test, Innova Rabin Cone Contrast, Konan–Waggoner D15 (KWC-D15), and Color Assessment and Diagnosis (CAD). Sixty-eight color-vision-defective persons participated. The KWC-D15 had the highest AC1 with the F-D15 ( A C 1 = 0.88 ). Both the CAD and OCCT had the highest values with the HWA ( A C 1 > 0.96 ). The KWC-D15 would be the best substitute for the F-D15. Either the CAD or OCCT would be appropriate substitutes for the HWA.

Human performance measures were used to evaluate the perceptual processing efficiency of infrared and fused-infrared images. In two experiments, eye movements were recorded while subjects searched for and identified human targets in forested scenes presented on a computer monitor. The scenes were photographed simultaneously using short-wave infrared (SWIR), long-wave infrared (LWIR), and visible (VIS) spectrum cameras. Fused images were created through two-way combinations of these single-band images. In Experiment 1 the single band sensors were contrasted with a simple average fusion scheme (SWIR/LWIR). Analysis of subjects’ eye movements revealed differences between sensors in measures of central processing (gaze duration, response accuracy) and peripheral selection (detection interval, saccade amplitude). In Experiment 2 this methodology was applied to compare three two-way combinations of sensors (SWIR/LWIR, SWIR/VIS, VIS/LWIR), produced by state-of-the-art fusion methods. Peripheral selection for fused images tended to exhibit a compromise between the performance levels of component sensor images, while measures of central processing showed evidence that fused images matched or exceeded the performance level of component single-band sensor images. Stimulus analysis was conducted to link measures of central and peripheral processing efficiency to image characteristics (e.g. target contrast, target-background contrast), and these image characteristics were able to account for a moderate amount of the variance in the performance across fusion conditions. These findings demonstrate the utility of eye movement measures for evaluating the perceptual efficiency of fused imagery.

Prior research has shown that task instructions influence the locations and durations of eye fixations during scene viewing. These task-related changes in gaze patterns are likely to be associated with a top-down influence of attention. Presently we applied a saccadic-inhibition manipulation in order to detect another expected manifestation of top-down attention: perceptual enhancement. Participants viewed eight-item arrays containing photographs from two categories of scenes. Four of the photos depicted natural landscapes (“nature”) and the other four depicted urban environments (“buildings”). Participants were instructed to memorize scenes from one of the categories in preparation for a later recognition memory test. During eye fixations the border around the fixated scene flickered briefly from black to white with a random interval between flickers ranging from 400 to 600 ms. We computed the likelihood of a saccade being initiated in the period following the flicker. Consistent with prior research, we found a strong saccadic inhibition effect with maximum saccadic inhibition occurring approximately 97 ms following the flicker. Importantly, the saccadic inhibition effect was stronger and longer lasting when the subject’s eyes were fixated on a relevant scene compared to an irrelevant scene. These findings are consistent with perceptual enhancement as a result of top-down attention.

Objective We examined the contribution of binocular vision and experience to performance on a simulated helicopter flight task. Background Although there is a long history of research on the role of binocular vision and stereopsis in aviation, there is no consensus on its operational relevance. This work addresses this using a naturalistic task in a virtual environment. Method Four high-resolution stereoscopic terrain types were viewed monocularly and binocularly. In separate experiments, we evaluated performance of undergraduate students and military aircrew on a simulated low hover altitude judgment task. Observers were asked to judge the distance between a virtual helicopter skid and the ground plane. Results Our results show that for both groups, altitude judgments are more accurate in the binocular viewing condition than in the monocular condition. However, in the monocular condition, aircrew were more accurate than undergraduate observers in estimating height of the skid above the ground. Conclusion At simulated altitudes of 5 ft (1.5 m) or less, binocular vision provides a significant advantage for estimation of the depth separation between the landing skid and the ground, regardless of relevant operational experience. However, when binocular cues are unavailable aircrew outperform undergraduate observers, a result that likely reflects the impact of training on the ability to interpret monocular depth cues.

The problem of predicting real-world operator performance with digital imaging devices is of great interest within the military and commercial domains. There are several approaches to this problem, including: field trials with imaging devices, laboratory experiments using imagery captured from these devices, and models that predict human performance based on imaging device parameters. The modeling approach is desirable, as both field trials and laboratory experiments are costly and time-consuming. However, the data from these experiments is required for model validation. Here we considered this problem in the context of dismounted soldiering, for which detection and identification of human targets are essential tasks. Human performance data were obtained for two-alternative detection and identification decisions in a laboratory experiment in which photographs of human targets were presented on a computer monitor and the images were digitally magnified to simulate range-to-target. We then compared the predictions of different performance models within the NV-IPM software package: Targeting Task Performance (TTP) metric model and the Johnson model. We also introduced a modification to the TTP metric computation that incorporates an additional correction for target angular size. We examined model predictions using NV-IPM default values for a critical model constant, V50, and we also considered predictions when this value was optimized to fit the behavioral data. When using default values, certain model versions produced a reasonably close fit to the human performance data in the detection task, while for the identification task all models substantially overestimated performance. When using fitted V50 values the models produced improved predictions, though the slopes of the performance functions were still shallow compared to the behavioral data. These findings are discussed in relation to the models’ designs and parameters, and the characteristics of the behavioral paradigm.

We developed a variant of the single fixation replacement paradigm (Yang & McConkie, 2001, 2004) in order to examine the effect of stimulus quality on fixation duration during reading. Subjects’ eye movements were monitored while they read passages of text for comprehension. During critical fixations, equal changes to the luminance of the background produced either an increase (Up-Contrast) or a decrease (Down-Contrast) of the contrast of the text. The durations of critical fixations were found to be lengthened in the Down-Contrast but not the Up-Contrast condition. Ex-Gaussian modelling of the distributions of fixation durations showed that the reduction in stimulus quality lengthened the majority of fixations, and a survival analysis estimated the onset of this effect to be approximately 141 ms following fixation onset. Because the stimulus quality of the text during critical fixations could not be predicted or parafoveally previewed prior to foveation, the present effect can be attributed to an immediate effect of stimulus quality on fixation duration.

Participants' eye movements were monitored in two visual search experiments that manipulated target-distractor similarity (high vs. low) as well as the availability of distractors for extrafoveal processing (Free-Viewing vs. No-Preview). The influence of the target-distractor similarity by preview manipulation on the distributions of first fixation and second fixation duration was examined by using a survival analysis technique which provided precise estimates of the timing of the first discernible influence of target-distractor similarity on fixation duration. We found a significant influence of target-distractor similarity on first fixation duration in normal visual search (Free Viewing) as early as 26–28 ms from the start of fixation. In contrast, the influence of target-distractor similarity occurred much later (199–233 ms) in the No-Preview condition. The present study also documented robust and fast acting extrafoveal and foveal preview effects. Implications for models of eye-movement control and vi...

Prior research has demonstrated that during two-alternative decision making, gaze is biased towards the alternative that is eventually chosen. The Gaze Cascade model proposed by Shimojo, Simion, Shimojo, and Scheier (2003) predicts a larger bias for decisions requiring one to choose the item that is liked the most versus decisions that require one to choose the item that is disliked most. More recently, Park, Shimojo, and Shimojo (2010) showed that preference formation operates differently during decisions among faces and scenes, which suggests that gaze bias might differ depending on whether the decision stimuli are faces or scenes. In the present study we tested these two hypotheses in a within-subject design. Eye movements were monitored while participants (n = 48) made two-alternative Like or Dislike decisions among pairs of faces or scenes. We found remarkably little influence of stimulus type on gaze bias for either decision task, which disconfirms the hypothesis that gaze bias operates differently ...

The present study employed a saccade-contingent change paradigm to investigate the effect of spatial frequency filtering on fixation durations during scene viewing. Subjects viewed grayscale scenes while encoding them for a later memory test. During randomly chosen saccades, the scene was replaced with an alternate version that remained throughout the critical fixation that followed. In Experiment 1, during the critical fixation, the scene could be changed to high-pass and low-pass spatial frequency filtered versions. Under both conditions, fixation durations increased, and the low-pass condition produced a greater effect than the high-pass condition. In subsequent experiments, we manipulated the familiarity of scene information during the critical fixation by flipping the filtered scenes upside down or horizontally. Under these conditions, we observed lengthening of fixation durations but no difference between the high-pass and low-pass conditions, suggesting that the filtering effect is related to the mismatch between information extracted within the critical fixation and the ongoing scene representation in memory. We also conducted control experiments that tested the effect of changes to scene orientation (Experiment 2a) and the addition of color to a grayscale scene (Experiment 2b). Fixation distribution analysis suggested two effects on the distribution fixation durations: a fast-acting effect that was sensitive to all transsaccadic changes tested and a later effect in the tail of the distribution that was likely tied to the processing of scene information. These findings are discussed in the context of theories of oculomotor control during scene viewing.

Participants’ eye movements were monitored in an experiment that manipulated the frequency of target words (high vs. low) as well as their availability for parafoveal processing during fixations on the pre-target word (valid vs. invalid preview). The influence of the word-frequency by preview validity manipulation on the distributions of first fixation duration was examined by using ex-Gaussian fitting as well as a novel survival analysis technique which provided precise estimates of the timing of the first discernible influence of word frequency on first fixation duration. Using this technique, we found a significant influence of word frequency on fixation duration in normal reading (valid preview) as early as 145 ms from the start of fixation. We also demonstrated an equally rapid non-lexical influence on first fixation duration as a function of initial landing position (location) on target words. The time-course of frequency effects, but not location effects was strongly influenced by preview validity, demonstrating the crucial role of parafoveal processing in enabling direct lexical control of reading fixation times. Implications for models of eye-movement control are discussed.

Participants' eye movements were monitored in two scene viewing experiments that manipulated the task-relevance of scene stimuli and their availability for extrafoveal processing. In both experiments, participants viewed arrays containing eight scenes drawn from two categories. The arrays of scenes were either viewed freely (Free Viewing) or in a gaze-contingent viewing mode where extrafoveal preview of the scenes was restricted (No Preview). In Experiment 1a, participants memorized the scenes from one category that was designated as relevant, and in Experiment 1b, participants chose their preferred scene from within the relevant category. We examined first fixations on scenes from the relevant category compared to the irrelevant category (Experiments 1a and 1b), and those on the chosen scene compared to other scenes not chosen within the relevant category (Experiment 1b). A survival analysis was used to estimate the first discernible influence of the task-relevance on the distribution of first-fixation d...

Over the past half century, research on human decision making has expanded from a purely behaviorist approach that focuses on decision outcomes, to include a more cognitive approach that focuses on the decision processes that occur prior to the response. This newer approach, known as process tracing, has employed various methods, such as verbal protocols, information search displays, and eye movement monitoring, to identify and track psychological events that occur prior to the response (such as cognitive states, stages, or processes). In the present article, we review empirical studies that have employed eye movement monitoring as a process tracing method in decision making research, and we examine the potential of eye movement monitoring as a process tracing methodology. We also present an experiment that further illustrates the experimental manipulations and analysis techniques that are possible with modern eye tracking technology. In this experiment, a gaze-contingent display was used to manipulate stimulus exposure during decision making, which allowed us to test a specific hypothesis about the role of eye movements in preference decisions (the Gaze Cascade model; Shimojo, Simion, Shimojo, & Scheier, 2003). The results of the experiment did not confirm the predictions of the Gaze Cascade model, but instead support the idea that eye movements in these decisions reflect the screening and evaluation of decision alternatives. In summary, we argue that eye movement monitoring is a valuable tool for capturing decision makers’ information search behaviors, and that modern eye tracking technology is highly compatible with other process tracing methods such as retrospective verbal protocols and neuroimaging techniques, and hence it is poised to be an integral part of the next wave of decision research.

Word properties like imageability and word frequency improve cued recall of verbal paired-associates. We asked whether these enhancements follow simply from prior effects on item-memory, or also strengthen associations between items. Participants studied word pairs varying in imageability or frequency: pairs were “pure” (high–high, low–low) or “mixed” (high–low, low–high) where “high” and “low” refer to imageability or frequency values and are probed with forward (A–?) and backward (?–B) cues. Probabilistic model fits to the data suggested that imageability primarily improved retrieval of associations, but frequency primarily improved recall of target items. All pair types exhibited a high correlation between forward and backward probe accuracy, a measure of holistic learning ( Kahana, 2002 ), which extends the boundary conditions of holistic association-memory and challenges Paivio’s (1971) suggestion that holistic learning depends critically on imagery. In sum, item properties can boost association-memory beyond simply boosting target retrievability.

In three experiments, we used eyetracking to investigate the time course of biases in looking behaviour during visual decision making. Our study replicated and extended prior research by Shimojo, Simion, Shimojo, and Scheier (2003), and Simion and Shimojo (2006). Three groups of participants performed forced-choice decisions in a two-alternative free-viewing condition (Experiment 1a), a two-alternative gaze-contingent window condition (Experiment 1b), and an eight-alternative free-viewing condition (Experiment 1c). Participants viewed photographic art images and were instructed to select the one that they preferred (preference task), or the one that they judged to be photographed most recently (recency task). Across experiments and tasks, we demonstrated robust bias towards the chosen item in either gaze duration, gaze frequency or both. The present gaze bias effect was less task specific than those reported previously. Importantly, in the eight-alternative condition we demonstrated a very early gaze bias...

Two of the most well studied and ecologically relevant memory paradigms are memory for pairs (“associations”) and ordered sequences (“serial lists”). Behavioral theories comprise two classes: those that use common mechanisms and those that use distinct mechanisms for study and retrieval of associations versus serial lists. We tested the common-mechanisms hypothesis by recording electroencephalographic activity related to successful study (“subsequent memory effect” [SME]) of pairs and short lists (triples) of nouns. Multivariate analysis identified four distributed patterns of brain activity: (1) right parietal activity throughout most of the study period that differentiated study of pairs from triples within subjects as well as exhibiting an SME that was significant for pairs but not for triples; (2) a left parietal and fronto-polar activity pattern that was reliable around 500 msec and later in the study trial, exhibiting an SME for pairs and a weaker, nonsignificant SME for triples; (3) a left frontal/right parietal topography in the middle of the study interval which covaried with speed and accuracy across subjects; and (4) a pattern resembling the late positive component preceded by an early potential which together covaried with accuracy in triples but slow response times for both pairs and triples. These patterns point to the relevance of three classic SME components (early, late positive, and slow components) from single-item memory to memory for structured information, but suggest that they reflect subsets of more complex spatio-temporal patterns. Our findings support common underlying mechanisms for study and recall of pairs and lists. However, existing models must be modified to account for differences in both the presence of certain study-relevant processes and in the relevance of these processes to performance measures for pairs versus serial lists.

We tested predictions derived from the gaze cascade model of preference decision making (Shimojo, Simion, Shimojo, & Scheier, 2003; Simion & Shimojo, 2006, 2007). In each trial, participants’ eye movements were monitored while they performed an eight-alternative decision task in which four of the items in the array were preexposed prior to the trial. Replicating previous findings, we found a gaze bias toward the chosen item prior to the response. However, contrary to the prediction of the gaze cascade model, preexposure of stimuli decreased, rather than increased, the magnitude of the gaze bias in preference decisions. Furthermore, unlike the prediction of the model, preexposure did not affect the likelihood of an item being chosen, and the pattern of looking behavior in preference decisions and on a nonpreference control task was remarkably similar. Implications of the present findings in multistage models of decision making are discussed.

Rhythmic brain activity has been implicated in learning and memory. Many models implicate theta oscillations (4–8 Hz) specifically in learning of relational information such as pairings and ordered lists. We tested this hypothesis in humans by recording electroencephalographic activity while participants studied nouns organised into pairs or triples for a later cued recall test. If theta is critical in learning structured information, then the amount of theta activity present during study of pairs and triples should covary with subsequent memory performance (accuracy and response times). Multivariate partial least squares analysis revealed three patterns of oscillatory activity associated with task conditions in different ways: a) Within subjects, successful study of pairs but not triples was associated with elevations in oscillations at multiple frequencies including theta, b) Frontal theta oscillations, in conjunction with beta oscillations, covaried with memory performance across subjects for both pairs and triples and c) Right-lateralized gamma oscillations in conjunction with low-frequency oscillations were associated with faster responding at the expense of accuracy across subjects for both pairs and triples. These findings support models that implicate theta oscillations in learning structured information rather than item information alone but similar to prior reports, suggest that theta oscillations explain individual variability better than trial-to-trial variability in behavior.

Paired associates and serial list memory are typically investigated separately. An "isolation principle" (J. B. Caplan, 2005) was proposed to explain behavior in both paradigms by using a single model, in which serial list and paired associates memory differ only in how isolated pairs of items are from interference from other studied items. In the present study, 2 experiments identify a critical dissociation between the 2 paradigms, challenging this unified account. Specifically, forward and backward probes were highly correlated for pairs and less so for short lists (triples). The authors asked whether the isolation principle could quantitatively accommodate this type of dissociation. A simulation confirmed that a single model incorporating the isolation principle can adequately explain this and other dissociations, supporting the common processes view.

We employed a variant of the mask-onset delay paradigm in order to limit the availability of visual information in central and peripheral vision within individual fixations during scene viewing. Subjects viewed full-color scene photos with instructions to search for a target object (Experiment 1) or to study them for a later memory test (Experiment 2). After a fixed interval following the onset of each eye fixation (50-100 ms), the scene was scrambled either in the central visual field or over the entire display. The intact scene was presented when the subject made an eye movement. Our results reconcile different sets of findings from prior research regarding the masking of central and peripheral visual information at different intervals following fixation onset. In particular, we found that when the entire display was scrambled, both search and memory performance were impaired even at relatively long mask-onset intervals. In contrast, when central vision was scrambled, there were subtle impairments that depended on the viewing task. In the 50-ms mask-onset interval, subjects were selectively impaired at identifying, but not in locating, the search target (Experiment 1), while memory performance (Experiment 2) was unaffected in this condition, and hence, the reliance on central and peripheral visual information depends partly on the viewing task.

In two experiments, participants solved anagram problems while their eye movements were monitored. Each problem consisted of a circular array of five letters: a scrambled four-letter solution word containing three consonants and one vowel, and an additional randomly-placed distractor consonant. Viewing times on the distractor consonant compared to the solution consonants provided an online measure of knowledge of the solution. Viewing times on the distractor consonant and the solution consonants were indistinguishable early in the trial. In contrast, several seconds prior to the response, viewing times on the distractor consonant decreased in a gradual manner compared to viewing times on the solution consonants. Importantly, this pattern was obtained across both trials in which participants reported the subjective experience of insight and trials in which they did not. These findings are consistent with the availability of partial knowledge of the solution prior to such information being accessible to subjective phenomenal awareness.

Anticipatory deployment of attention may operate through networks of brain areas that modulate the representations of to-be-attended items in advance of their occurrence through top-down control. Luks and Simpson (2004) (Luks, T.L., Simpson, G.V., 2004. Preparatory deployment of attention to motion activates higher order motion-processing brain regions. NeuroImage 22, 1515-1522) found activations in both control areas and sensory areas during anticipatory deployment of attention to visual motion in the absence of stimuli. In the present follow-up analysis, we tested which network activity during anticipatory deployment of attention is functionally connected with task-related network activity during subsequent selective processing of motion stimuli. Following a cue (anticipatory phase), participants monitored a sequence of complex motion stimuli for a target motion pattern (task phase). We analyzed fMR signal using a partial least squares analysis with previously identified cue- and motion-related voxels as seed regions. The method identified two networks that covaried with the activity of seed regions during the cue and motion-stimulus-processing phases of the task. We suggest that the first network, involving ventral intraparietal sulcus, superior parietal lobule and motor areas, is related to anticipatory and sustained visuomotor attention. Operating in parallel to this visuomotor attention network, there is a second network, involving visual occipital areas, frontal areas as well as angular and supramarginal gyri, that may underlie anticipatory and sustained visual attention processes.

Participants' eye movements were monitored while they viewed displays containing 6 exemplars from one of several categories of everyday items (belts, sunglasses, shirts, shoes), with a column of 3 items presented on the left and another column of 3 items presented on the right side of the display. Participants were either required to choose which of the two sets of 3 items was the most expensive (2-AFC) or which of the 6 items was the most expensive (6-AFC). Importantly, the stimulus display, and the relevant stimulus dimension, were held constant across conditions. Consistent with the hypothesis of top-down control of eye movements during visual decision making, we documented greater selectivity in the processing of stimulus information in the 6-AFC than the 2-AFC decision. In addition, strong spatial biases in looking behavior were demonstrated, but these biases were largely insensitive to the instructional manipulation, and did not substantially influence participants' choices.