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Essential tremor (ET) is a common movement disorder affecting the performance of various daily tasks, including drawing. While spiral-drawing task characteristics have been described among patients with ET, research about the significance of the drawing direction of both spiral and lines tasks on the performance process is scarce. This study mapped inter-group differences between people with ET and controls related to drawing directions and the intra-effect of the drawing directions on the tremor level among people with ET. Twenty participants with ET and eighteen without ET drew spirals and vertical and horizontal lines on a digitizer with an inking pen. Time-based outcome measures were gathered to address the effect of the drawing directions on tremor by analyzing various spiral sections and comparing vertical and horizontal lines. Significant group differences were found in deviation of the spiral radius from a filtered radius curve and in deviation of the distance curve from a filtered curve for both line types. Significant differences were found between defined horizontal and vertical spiral sections within each group and between both line types within the ET group. A significant correlation was found between spiral and vertical line deviations from filtered curve outcome measures. Achieving objective measures about the significance of drawing directions on actual performance may support the clinical evaluation of people with ET toward developing future intervention methods for improving their functional abilities.

The vertical-horizontal illusion is the overestimation of a vertical line compared to a horizontal line of the same length. Jackson and Cormack (2007) proposed that the vertical-horizontal illusion might be a byproduct of the mechanisms that generate the environmental vertical illusion, which is the tendency to overestimate vertical distances (i.e., heights) relative to horizontal distances the same length. In our study, 326 undergraduate participants stood atop an 18.6-meter parking structure and estimated both the height of the structure and the horizontal distance of a target placed 18.6 meters away, using a moveable horizontal target across the length of the structure. Participants also completed a vertical-horizontal illusion task by drawing a horizontal line below a 9.1 cm vertical line. We correlated vertical distance estimates with vertical line estimates to test Jackson and Cormack’s byproduct hypothesis. This hypothesis was very weakly—if at all—supported by the data: Participants’ overestimations in the vertical-horizontal illusion task explained 1% of the variance associated with their overestimations in the environmental vertical illusion task. Additionally, to test whether the environmental vertical illusion is impervious to explicit awareness, a random half of our participants were advised to be mindful that people tend to overestimate heights. The results supported our second hypothesis: Even when participants were made aware of the environmental vertical illusion, they still reliably overestimated heights. Discussion addressed implications for the robustness of the environmental vertical illusion (e.g., treatment of those with acrophobia).

Knowledge of target features can guide attention in many conjunction searches in a top-down manner. For example, in search of a red vertical line among blue vertical and red horizontal lines, observers can guide attention toward all red items and all vertical items. In typical conjunction searches, distractors often form perceptually vivid, categorical groups of identical objects. This could favor the efficient search via guidance of attention to these "segmentable" groups. Can attention be guided if the distractors are not neatly segmentable (e.g., if colors vary continuously from red through purple to blue)? We tested search for conjunctions of color × orientation (Experiments 1, 3, 4, 5) or length × orientation (Experiment 2). In segmentable conditions, distractors could form two clear groups (e.g., blue steep and red flat). In non-segmentable conditions, distractors varied smoothly from red to blue and/or steep to flat; thus, discouraging grouping and increasing overall heterogeneity. We found that the efficiency of conjunction search was reasonably high and unaffected by segmentability. The same lack of segmentability had a detrimental effect on feature search (Experiment 4) and on conjunction search, if target information was limited to one feature (e.g., find the odd item in the red set, "subset search," Experiment 3). Guidance in conjunction search may not require grouping and segmentation cues that are very important in other tasks like texture discrimination. Our results support an idea of simultaneous, parallel top-down guidance by multiple features and argue against models suggesting sequential guidance by each feature in turn.

Weightlifting technique can be objectively assessed from two-dimensional video recordings. Despite its importance, participants' bar trajectories in research involving the snatch or clean exercises are often not reported, potentially due to the time required to digitize video. The purpose of this investigation was to evaluate the use of a light-emitting diode (LED)-based marker, digital video, and open-source software to automatically track the bar end during weightlifting exercises. A former national-level weightlifter was recorded with a digital video camera performing the snatch, clean and jerk, and squat exercises. An LED-based marker was placed on the right end of the bar. This marker was automatically tracked using 2 open-source software programs to obtain vertical and horizontal position coordinates. The LED-based marker was successfully auto-tracked for all videos over a variety of camera settings. Furthermore, the vertical and horizontal bar displacements and vertical bar velocity were consistent between the 2 software programs. This study demonstrates that an LED-based marker can be automatically tracked using open-source software. This combination of an LED-based marker, consumer camera, and open-source software is an accessible, low-cost method to objectively evaluate weightlifting technique.

L-shaped configuration is a commonly used stimulus configuration in studying horizontal vertical illusion. Here, we report that the horizontal vertical illusion is substantially underestimated when the L-shaped configuration is used for evaluating the illusion. Experiment 1 found that, in a length perception task, the perceived length of a vertical bar was about 10% longer than that of a horizontal bar with the same physical size. Similar amount of HVI was found in a length comparison task, in which the length of a horizontal bar was compared to that of a vertical bar and the two bars were presented separately in space or in time. In contrast, when the length comparison task was conducted with the two bars being arranged in a connected L-shape, the illusion was halved in strength. Experiment 2 and 3 studied what might be the cause of this L-shape induced HVI-underestimation. Two factors were investigated: the connectedness of the two lines, and the 45° absolute orientation or the 45° inner angle information embedded in the upright isosceles L-shape. The results showed that the HVI strength was not much affected when the 45° absolute orientation and the 45° angle information was made useless for the length comparison task. In contrast, the illusion was significantly reduced in strength whenever the two lines were separated as compared to when they were connected. These results suggested that the connectedness of the two lines must underlie the underestimation of the horizontal vertical illusion in the L-shaped configurations.

International audience; The evolution of languages shares certain characteristics with that of genes, such as the predominantly vertical line of transmission and the retention of traces of past events such as contact. Thus, studies of language phylogenies and their correlations with genetic phylogenies can enrich our understanding of human prehistory, while insights gained from genetic studies of past population contact can help shed light on the processes underlying language contact and change. As demonstrated by recent research, these evolutionary processes are more complex than simple models of gene-language coevolution predict, with linguistic boundaries only occasionally functioning as barriers to gene flow. More frequently, admixture takes place irrespective of linguistic differences, but with a detectable impact of contact-induced changes in the languages concerned.

The purpose of this study was to examine graph comprehension in college students with developmental dyslexia. We investigated how graph types (line, vertical bar, and horizontal bar graphs), graphic patterns (single and double graphic patterns), and question types (point locating and comparison questions) differentially affect graph comprehension of students with and without dyslexia. Groups were compared for (1) reaction times for answering comprehension questions based on graphed data and (2) eye gaze times for specific graph subregions (x-axis, y-axis, pattern, legend, question, and answer). Dyslexic readers were significantly slower in their graph comprehension than their peers with group differences becoming more robust with the increasing complexity of graphs and tasks. In addition, dyslexic readers' initial eye gaze viewing times for linguistic subregions (question and answer) and total viewing times for both linguistic (question and answer) and nonlinguistic (pattern) subregions were significantly longer than their control peers' times. In spite of using elementary-level paragraphs for comprehension and simple graph forms, young adults with dyslexia needed more time to process linguistic and nonlinguistic stimuli. These findings are discussed relative to theories proposed to address fundamental processing deficits in individuals with dyslexia.

Background Normal adults demonstrate a slight upward bias (vertical pseudoneglect) when attempting vertical line bisection. The mechanism for this bias is unknown. Activation of the allocentric (object-centered) ventral visual system during attempted bisection may induce this bias. This object-centered ventral stream may also mediate focal attention. As compared to bisection, when normal participants perform a vertical line quadrisection task that requires more focal attention, they may have a greater upward bias. Methods Sixteen participants bisected and quadrisected vertical lines. Results The mean upward bias (deviation error) for the quadrisection tasks was significantly higher than the mean error for the line bisections. Conclusions These results are consistent with the hypothesis that activation of the ventral stream by a task that requires focal allocentric attention can induce an upward vertical bias that is greater than the upward bias observed with allocentric line bisection, a task that requires more global attention.

Although commonly prescribed, little research exists on bath grab bars. This study examined the use of bath grab bars following an experimentally induced balance perturbation, the influence of the task on grab bar use, and the influence of balance loss on acceptance of grab bars. A mixed design documented the use of four different grab bar configurations: (a) no bars, (b) vertical/horizontal combination, (c) L-shaped bar, and (d) vertical/angled combination following balance loss. Eighty adults were randomly assigned to three groups. Each group tried the "no bar" configuration and one of the other grab bar configurations. In 25% of the trials for each configuration, balance perturbation was induced. Older adults used grab bars 59.4% of time to regain balance, compared to 13.6% for younger adults. The vertical bar on the side wall was favored by both groups of participants during both bathtub entry and exit. To promote safety in the home, existing building codes must be revised to recommend minimally a vertical grab bar on the side wall. Additional bars may be needed to ensure safety during stand-to-sit and sit-to-stand phases of bath transfers. Initiatives must be taken to decrease the prejudice associated with grab bars.

Can a mind accommodate two time lines? Miles, Tan, Noble, Lumsden and Macrae (Psychonomic Bulletin & Review 18, 598-604, 2011) shows that Mandarin-English bilinguals have both a horizontal space-time mapping consistent with linguistic conventions within English and a vertical representation of time commensurate with Mandarin. However, the present study, via two experiments, demonstrates that Mandarin monolinguals possess two mental time lines, i.e., one horizontal and one vertical line. This study concludes that a Mandarin speaker has two mental time lines not because he/she has acquired L2 English, but because there are both horizontal and vertical expressions in Mandarin spatiotemporal metaphors. Specifically, this study highlights the fact that a horizontal time line does exist in a Mandarin speaker's cognition, even if he/she is a Mandarin monolingual instead of a ME bilingual. Taken together, the evidence in hand is far from sufficient to support Miles et al.'s (2011) conclusion that ME bilinguals' horizontal concept of time is manipulated by English. Implications for theoretical issues concerning the language-thought relationship in general and the effect of bilingualism on cognition in particular are discussed.

Four experiments examined the biases of individual subjects when attempting to bisect vertical lines, and tested various hypotheses concerning the origin of vertical bisection errors (VBEs). In each experiment, individual differences on the vertical line bisection task were compared to individual differences on another task to evaluate whether the tasks were systematically related. In the first experiment, VBEs were found not to correlate with horizontal line bisection errors (HBEs). In the second experiment, VBEs were found not to correlate with the size of the horizontal-vertical illusion (HVI). In the third experiment, VBEs were found not to correlate with differences in perceived length of vertical lines presented in the upper and lower visual fields that were displaced horizontally. In the fourth experiment, VBEs were found to correlate with bisection errors of an open vertical interval. The results of the first three studies are counter to various hypotheses of the origins of vertical bisection errors. The last experiment suggests that lines, per se, are unnecessary for VBEs. Rather, it is important that the upper and lower segments of the stimulus that are judged to be equal on vertical bisection tasks are co-extensive.

We investigated the conditions that underlie the vertical and bisection illusion in touch, in order to understand the basis of their similarity to visual illusions, and the means of reducing the biases in length perception by active touch. Movement, speed, and spatial reference cues were tested. Movements in scanning L-shapes in ipsilateral and contralateral (across the body midline) table-top space produced significant underestimation of the vertical line with the right hand, but not with the left hand. Right-handed scanning of L-shapes showed no significant bias when the vertical line in the figure was aligned to the body midline, suggesting that spatial cues were involved. The vertical line was overestimated in inverted T-shapes, but underestimated in rotated T-shapes, implicating line bisection. Holding scanning latencies constant reduced the vertical error for inverted T-shapes, but could not explain the bisection bias. Sectioning biases were predicted by the location of junctions on sectioned lines, showing that junction points act as misleading anchor cues for movement extents. The illusion was significantly reduced when reference information was added by instructing subjects to relate two-handed scanning of the figure to an external frame and to body-centred cues. It is argued that disparities in spatial reference (anchor) cues for movement extents are involved in vertical and bisection biases in active touch. The hypothesis that length illusions depend on disparities in spatial reference information can also account for the similarity of the tactile to the visual horizontal – vertical illusion.

Thresholds for detecting the angle of rotation of vertical symmetrical patterns containing few or no explicit vertical or horizontal contours were found to be almost as low as those for an actual vertical line extending approximately the same range. This hyperacuity performance, which we refer to as implicit orientation discrimination, shares most of its properties with the orientation discrimination of explicit lines, suggesting a category of orientation processing whose neural mechanisms are related to those involved in the processing of straight contours and those underlying the detection of axes of symmetry. Strong binding effects between the components of the figures were demonstrated and their temporal interactions were also investigated. Our results have implications for possible neural interactions early in the cortical visual stream. © 1997 Elsevier Science Ltd. All rights reserved

International audience; IntroductionVerticality is essential in our life, especially for postural stability. Subjective vertical as well as postural stability depends on different sensorial information: visual, vestibular and somesthesic. They help to build the spatial referentials and create a central representation of verticality. Children are more visuo-dependant than adults; however, we did not find any study focusing on how children develop their sense of verticality.MethodsWe studied two groups of subjects: 10 children (from 6 to 8 years) and 12 young adults. We recorded postural stability with a Techno Concept plateform and perception of subjective visual vertical in the following conditions: while adjusting the vertical in the dark or with visual perturbation, while fixating the vertical bar, and with eyes closed.ResultsChildren are more instable than adults in terms of postural parameters, and also while performing a double task, especially when no visual references are present. They also present a higher variability and lower accuracy than adults in reporting their perception of true vertical reference.DiscussionChildren might have limited attentional resources, and focus their attention on the more demanding task, corresponding to the U-shaped non-linear model.

Whereas the ventral visual processing stream mediates facial and object recognition, the dorsal stream mediates recognition of spatial relationships. In addition, ventral lesions have been reported to induce visual inattention to the upper visual field and dorsal lesions inattention to the lower field. The purpose of this study is to test the hypothesis that activation of the ventral stream will induce an upward attentional bias and activation of the dorsal stream, a downward bias, as assessed by vertical line bisection tests. Twelve healthy right-handed individuals performed vertical line bisections. During these trials, either pictures of famous faces or dots in different spatial locations were presented above and below the line. The participants were asked to recognize and remember the faces or locations of dots while they performed the bisections. In control trials, they were no faces or dots. An upward bias was observed in all conditions. This upward bias was significantly increased in the face recognition and recall condition, but not altered in the dot location condition. Although the face task appeared to activate the ventral stream and increase the upward vertical bias, the failure of the dot localization task to alter the bias may be related task selection. Dorsolateral lesions cause optic ataxia, a disorder of the egocentric "where" system, and the dot location task in this study was allocentric. Thus, further research will be needed to learn whether an egocentric spatial localization task, with a memory component, will alter the vertical attentional bias.

Given an estimate of the binocular disparity between a pair of points and an estimate of the viewing distance, or knowledge of eye position, it should be possible to obtain an estimate of their depth separation. Here we show that, when points are arranged in different vertical geometric configurations across two intervals, many observers find this task difficult. Those who can do the task tend to perceive the depth interval in one configuration as very different from depth in the other configuration. We explore two plausible explanations for this effect. The first is the tilt of the empirical vertical horopter: Points perceived along an apparently vertical line correspond to a physical line of points tilted backwards in space. Second, the eyes can rotate in response to a particular stimulus. Without compensation for this rotation, biases in depth perception would result. We measured cyclovergence indirectly, using a standard psychophysical task, while observers viewed our depth configuration. Biases predicted from error due either to cyclovergence or to the tilted vertical horopter were not consistent with the depth configuration results. Our data suggest that, even for the simplest scenes, we do not have ready access to metric depth from binocular disparity. Preprint

In an inverted T figure, the vertical line is largely overestimated (Avery and Day in J Exp Psychol 81:376-380, 1969). This vertical overestimation results from the vertical and bisection biases. Line orientation biases length perception in the sense that the vertical line of a L shape is perceived as longer than the horizontal line of the same physical length. In the inverted T figure, the vertical line is overestimated because of its orientation but also because the horizontal line is bisected. In the current study, we used various two-line configurations to investigate the role of bisection a/symmetry in line length perception and its interaction with the vertical bias. Experiment 1 showed that symmetry and asymmetry of bisection have different consequences on line length perception, as previously shown by Wolfe et al. (Percept Psychophys 67:967-979, 2005). Experiments 2 focused on the relation between the vertical and bisection biases by manipulating orthogonally line orientation and bisection a/symmetry. The results provided evidence that bisection can prevent the manifestation of the vertical bias, so that when the two lines are bisected, vertical lines are not anymore overestimated. These results are discussed in the light of recent findings claiming that saccades could play an essential role in length perception.

The study presents a simple method to predict the drawing performance of designers or artists by measuring the stability of their line drawings. An 8 x 3 two-way factorial design experiment with directions and phases was conducted to explore the most stable direction and phase among eight directions and three phases of line drawing. The scores of 40 participants' drawings rated by instructors were used directly as drawing performance. Correlations estimated relations of stability of the line drawing and drawing performance. Analyses showed 45 degrees was the most stable direction, whereas the least stable was 135 degrees. For each line drawing, the start was more stable than the middle and end phases. For drawing a plus sign (+), the horizontal line was more stable than the vertical line. When drawing a horizontal line, drawing rightward was more stable than drawing leftward; when drawing a vertical line, drawing downward was more stable than drawing upward. In general, drawing a multiplication sign (x) was similar to drawing a plus sign rotated counterclockwise with an angle of 45 degrees. Line-drawing stability was positively correlated with drawing performance, so line-drawing stability could be used to predict drawing performance. The stability of the least stable direction was the most powerful predictor for assessing drawing performance. All subjects were design students, were right-handed, and drew with the right hand. Persons from other fields and drawing with the nondominant hand are interesting topics for further investigation.

We present new experimental and mathematical techniques aimed at determining the features used in visual object recognition. We conceive of these features as the parts of an object that are treated as unitary wholes when recognizing or discriminating visual objects. For example, consider a task classifying a visual target presented in pixel noise as a "P" or a "Q". The features may correspond to particular shapes of the target letters. Two such features for "P", for example, might be a vertical line and upper-right-facing curve. The decision may be encoded in terms of particular values of such features, and an appropriate combination of these values may determine how the expression is perceived. We utilize recent advances in statistical machine learning techniques to uncover the features used by human observers.

The spatial representation abilities of 3- to 4-month-old infants were examined in four experiments. Experiments 1 and 2 showed that infants familiarized with a diamond appearing in distinct locations to the left or right of a vertical bar subsequently preferred a stimulus depicting the diamond on the opposite side of the bar over a stimulus depicting the diamond in a novel location on the same side of the bar. Experiment 3 was a replication of Experiment 1, except that the bar was oriented at 45 degrees. In this instance, infants divided their attention between the stimulus depicting the diamond on the opposite side of the bar and the stimulus depicting the diamond in a novel location on the same side of the bar. Experiment 4 demonstrated that the results of Experiment 3 were not a consequence of a failure to process the diagonal bar. When considered with previous reports that infants can represent the categories of above and below (Quinn, 1994), the present results suggest that (1) infants can also represent the categories of left and right, and (2) performance cannot be interpreted as a response to an arbitrary crossing of one object relative to another. Although recent discussions of the relation between language and cognition have pointed to the ways in which spatial language influences spatial cognition (BowermanLevinson, 2001), the present findings are consistent with an influence in the opposite direction: Spatial cognition may in some instances shape spatial language.

This study assessed whether feedback would improve performance on a horizontal vertical illusion task and whether such improvement would transfer to different forms of the illusion. Subjects shortened the extended vertical line of small, medium, and large inverted-T figures to be equal in length to the horizontal line before and after being shown a correctly adjusted medium-sized figure (visual feedback). Next, they were tested on three alternate forms of the illusion; a production task (drawing 1-in. lines in the horizontal and vertical planes), an adjustment task using L figures, and a task requiring them to choose which of several sailboat drawings had mast height equal to hull length. Prior to feedback, vertical lines were adjusted shorter than the horizontal lines on each size inverted-T figure. After feedback on the medium-size figure, experimental subjects were more accurate than the controls on each size inverted-T figure. The results suggest that transfer of illusion decrement was also obtained for the boat-selection and, to a lesser extent, the L-figure adjustment tasks but not to the line-production task. These findings are consistent with the notion that improvement after feedback is not due to structural changes in visual processing or to simple feedback-induced compensation in performance but involves some strategic or cognitive change in judging line length.

The ability of human beings to shift their vergence between multiple disparity stimuli was investigated. The stimulus was a stereogram consisting of a single bar (1× 0.3°) projected in the center of a larger circular pattern (28° dia) of dots (0.3° dia). In the initial condition, the subjects perceived a single bar in the center of a cluster of dots, all lying in a single depth plane. The subjects were instructed to fixate either the bar or one of the dots close to the bar. Stepwise changes of target-vergence of either the bar, or of all dots, or of both configurations in opposite directions, were imposed in a random sequence. Under these conditions, ocular vergence was controlled by the target-vergence of the selected target at all times, even if this implied a loss of binocular fusion for the non-selected target. The effect of target selection per se, without concomitant changes in retinal position of the selected target, was studied in two experienced subjects with stabilized image techniques. The subjects viewed a configuration containing short vertical bars placed at either side of a long vertical bar. The short bars on different sides of the long bar had opposite (crossed or uncrossed) disparities. After stabilization of the configuration while the subject fixated the long bar, subjects attempted to fixate the short bars alternatingly. Due to the stabilization the ensuing eye movements did not affect the retinal positions, and thus the disparity, of the bars. Attempted fixation of a para-foveally viewed, short bar induced vergence responses in the appropriate direction. These vergence responses would have reduced disparity of the selected target if this had not been stabilized, at the expense of increasing disparity of non-selected targets. From this result we conclude that, by the mechanism of target selection, disparity information of the selected target is gated to a subsystem processing disparity which controls vergence.

Two experiments measured line-dot alignment errors to either a long (2 deg 6 min) or short (12.7 min) oblique test line which was presented either in isolation or abutting a vertical inducing line. Alignment PSE's were obtained for a variety of line-dot separations at both the free end and at the intersect end of the test line, using a multiple randomly interleaved staircase technique. A number of aspects of the data were inconsistent with the hypothesis that alignment errors reflect whole-of-line changes in perceived orientation or intercept when the inducing line is present. Rather, the results were consistent with the notion that long lines are processed by integrating the outputs of analysers which respond to short line segments and that alignment errors reflect the differential weighting given to such analysers, depending upon the distance between the dot and the relevant segment of the line. An alternate hypothesis involving “cognitive mistracking” (Tong and Weintraub, 1974) could not be excluded by the results.

Undergraduate students in social science and architecture did not differ in their accuracy of adjusting the vertical lines of L and inverted-T figures to be equal to a 1-in. horizontal line (the adjustment task) or in producing a 1-in. long line in the vertical or horizontal plane on a blank sheet of paper (the production task). In the adjustment task vertical lines were made significantly shorter than the horizontal comparison line and the shortening of the vertical line was significantly greater for the inverted-T than for the L-figure. In the production task lines drawn in the horizontal plane did not differ significantly from 1 inch but those drawn in the vertical plane were significantly shorter than 1 inch. Further, the magnitude of this error was equal to that obtained with the inverted-T figure. These results demonstrate that, while line bisection (the bisection of the horizontal by the vertical in the inverted-T figure) contributes to the horizontal-vertical illusion, the illusion clearly exists in the absence of a comparison line and can be accounted for as an overestimation of the vertical line.

An experiment was performed which examined the role of figural orientation directly, and the role of an inappropriately invoked size-constancy mechanism indirectly, in the actuation and magnitude of the horizontal—vertical illusion. When the vertical line of the stimulus figure was aligned above the horizontal line, the illusory effect was significant and positive; in contrast, when the vertical line was located below the horizontal line, the illusion was negative. Under the assumption that a vertical line can appear as a foreshortened line in depth, these findings support an explanation based on the operation of a misapplied size-constancy mechanism.

The Horizontal-Vertical (HV) Illusion was examined in two studies in which subjects adjusted the vertical line in L-shaped and inverted-T figures or produced lines in the vertical and horizontal planes. On the adjustment tasks, vertical lines were made significantly shorter than horizontal comparison lines, especially for the inverted-T figure. On the production tasks, lines drawn in the vertical plane were significantly shorter than lines drawn in the horizontal plane. The adjusted and created lines of subjects receiving intertrial feedback on illusion magnitude were significantly more accurate and less variable than the estimations of control subjects. Performance on either task or figure type did not differ as a function of sex of subject. The present results show that the HV illusion exists in the absence of line bisection or a comparison line and results from the overestimation of vertical lines. These findings further clarify the relative contributions of the structural and strategy mechanisms in the formation of the Horizontal-Vertical Illusion.

The effect of convergence on the perceived size of a light disk presented against a dark background was investigated by means of a projector stereoscope with polarizing filters. The results obtained with four subjects indicate that the logarithm of matched size decreases linearly as the convergence angle increases. The effect of binocular disparity was also examined by presenting a vertical bar beside the disk, but this did not add to the convergence effect. The results of a previous study on binocular disparity were reinterpreted as an effect of convergence difference between two objects. Implications of the present findings to the phenomenon of size constancy were discussed.

This study attempted to determine the influence of the division (bisection of the horizontal line by the vertical line) and orientation (vertical line seems longer than horizontal line) factors on the vertical-horizontal illusion. 100 Ss were divided into two groups, one with knowledge of the division and orientation factors and the other group without knowledge of these factors. The results indicated that the amount of error for the group with knowledge was significantly smaller than for the group without knowledge.

The inverted-T illusion was studied by the magnitude estimation method. The horizontal line in the inverted T is perceptually shorter than the same horizontal line presented singly, and the vertical line in the inverted T is perceptually longer than the same vertical line presented singly. Thus, the inverted-T illusion is due to both a perceptual lengthening of the vertical line and a shortening of the horizontal line. In the light of these findings, current theories of the illusion seem to give unsatisfactory explanations. Systematic studies of the inverted-T illusion (Finger & Spelt, 1947; Kiinnapas, 1955) show that, in the adult, the vertical line is perceived as about 5%10% longer than the horizontal one. However, the classical methods of psychophysics (the methods of limits, of adjustment, and of constant stimuli) do not seem to answer one important question: Is the illusion due to a perceptual change in the vertical line alone, a change in the horizontal line alone, or concommitant changes in both. The experiment reported here was undertaken in order to find an answer to this question.

THERE is a well-known visual illusion in which a vertical line is judged as longer than a horizontal line of the same length. The illusion also holds, though attenuated, when lines are perceived tactually, even in blind subjects1. This communication is concerned with a similar error which is made when speed of movement is assessed tactually, but which does not show when the judgment is made visually.