Perception of symmetry in infancy.

Symmetrical visual patterns, particularly vertically symmetrical ones, are preferred and processed faster than asymmetrical patterns by adults. Results of 3 experiments with 61 4- and 12-mo-olds show that (a) 4-mo-old infants showed no preference for symmetry, but they processed vertically symmetrical patterns more efficiently than horizontally symmetrical or asymmetrical ones; and (b) by 12 mo, infants preferred vertical symmetry to horizontal symmetry and asymmetry. Thus, preference for symmetry seems to develop late, whereas recognition of vertical symmetry is innate, matures very quickly, or is learned very early. (37 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discrimination of simulated texture patterns on the human hand

1. Textures formed by periodic dot arrays are defined by the dot density, spacing, and angular orientation with respect to the direction of motion. In this report we evaluate the effects of the dot density (intensive cues) and arrangement (spatial cues) on the ability of human subjects to discriminate texture patterns scanned across an OPTACON tactile stimulator that selective stimulates rapidly adapting cutaneous mechanoreceptors. We compared dot arrays arranged on the index finger in specific patterns (horizontal, vertical, diamond, up diagonal, or down diagonal orientation) and spaced 4.8, 7.2, or 9.6 mm apart (high, medium, and low density) with the use of a two-alternative forced-choice protocol. 2. Textures are well discriminated when their elements are tightly spaced along one axis and widely spaced on all other axes. Humans distinguish textures that differ only in orientation with mean accuracy of 75% at low density and 65% at medium density, but discriminate high-density textures poorly (mean accuracy = 48%). Accuracy is related to the angular disparity between patterns, and to similarity of spacing and orientation along major and minor axes of the arrays. Vertical and horizontal patterns are more accurately distinguished than the oblique ones, and diamond arrays are the least well discriminated. Diagonal and diamond textures are often confounded, and the up and down diagonal patterns are confused with each other particularly as the texture density rises. The preference for the vertical and horizontal patterns may relate to an interaction between the orientation axis of the texture and its direction of motion across the skin. 3. Intensive cues provided by the total number of applied stimuli supplement the spatial cues inherent to the pattern orientation, because textures that differ in both spacing and orientation are discriminated better than those that differ only in orientation or spacing. Mean accuracy ranges from 96% for comparisons of high- and low-density textures, which differ in the total number of dots by a factor of 2, to 80% when medium-density patterns are compared with high- or low-density textures. 4. Textures that differ in density but not in orientation are less well discriminated than those of different orientation. For example, 82% of patterns that differ in both density and orientation are distinguished correctly in pairings of low- and medium-density textures, whereas those that differ only in density are discriminated correctly on 45% of trials. Subjects seem to use spatial rather than intensive cues when discriminating patterns of similar density, suggesting that the similarity of form (the spatial arrangement of the closely spaced dots) is more readily apparent than small differences in spacing along the axis of motion. 5. Subjects are most most successful in differentiating texture patterns when they are able to mentally picture the orientation and spacing of the pattern. We found a strong correlation between the subjects' ability to discriminate textures of a given spacing and their ability to identify the specific texture by matching it to the appropriate visual representation. Subjects are able to identify correctly all five orientations at low and medium densities, with mean accuracy of 76%, but recognize only the vertical arrays when high-density patterns are presented. The ability to image the textures is noteworthy, because subjects received no feedback about performance. 6. Spatial imaging of textures appears limited by the diameter of cutaneous receptive fields on the hand. We propose that the structural axis of a regular texture array results from perceptual linkage of adjacent elements along one principal axis by continuous bands of neural activity when their spacing is smaller than the receptive field diameter.(ABSTRACT TRUNCATED)     

Discrimination and memory for symmetry in young children.

Conducted 3 experiments to assess the development of symmetry perception in children between the ages of 4 and 6 yrs. Exp I employed a learning task in which 72 Ss were asked at different times to discriminate vertically symmetrical, obliquely symmetrical, and horizontally symmetrical holistic patterns from asymmetrical ones. Results reveal a developmental progression: 4-yr-olds discriminated only vertical; 5-yr-olds, vertical and horizontal; and 6-yr-olds, vertical, horizontal, and oblique. Exp II retested the 18 6-yr-olds with fragmented patterns of the different symmetries; these Ss regressed to the performance level of 4-yr-olds and only discriminated vertical. Exp III, conducted with 18 Ss, used a memory-production task with new vertical, oblique, horizontal, and asymmetrical patterns constructed to 4, 5, or 6 elements. Measures of the goodness and accuracy of Ss' reproductions were consistent with data from the discrimination-learning experiments in terms of age, stimulus orientation, and stimulus complexity. These studies support the view that vertical symmetry is special perceptually and developmentally and that, after vertical, horizontal predominates, followed by oblique. The role of symmetry in early perceptual development and the value of child–adult perceptual comparisons are discussed. (55 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of structure in infant visual pattern perception.

In Exp 1, 15 infants (aged 4 mo 2 days to 5 mo 9 days) were presented with a symmetrical (SYP) and an asymmetrical pattern (ASP), using a paired comparison preference technique. The SYPs represented vertical, horizontal, 2-fold, and 4-fold symmetry (SYM). 15 infants (aged 3 mo 29 days, to 5 mo 16 days) in Exp 2 additionally viewed patterns with 8-fold SYM, using the same procedure as Exp 1. Ss preferred patterns with multiple axes of bilateral SYM relative to ASPs. Also, vertically oriented single axis bilateral SYM was more salient than horizontally oriented SYM. The perception of structure appears to be basic to the functioning of the visual system. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rostral fastigial nucleus activity in the alert monkey during three-dimensional passive head movements

The fastigial nucleus (FN) receives vestibular information predominantly from Purkinje cells of the vermis. FN in the monkey can be divided in a rostral part, related to spinal mechanisms, and a caudal part with oculomotor functions. To understand the role of FN during movements in space, single-unit activity in alert monkeys was recorded during passive three-dimensional head movements from rostral FN. Seated monkeys were rotated sinusoidally around a horizontal earth-fixed axis (vertical stimulation) at different orientations 15 degrees apart (including roll, pitch, vertical canal plane and intermediate planes). In addition, sinusoidal rotations around an earth-vertical axis (yaw stimulus) included different roll and pitch positions (+/-10 degrees, +/-20 degrees). The latter positions were also used for static stimulation. One hundred fifty-eight neurons in two monkeys were modulated during the sinusoidal vertical search stimulation. The vast majority showed a uniform response pattern: a maximum at a specific head orientation (response vector orientation) and a null response 90 degrees apart. Detailed analysis was obtained from 111 neurons. On the basis of their phase relation during dynamic stimulation and their response to static tilt, these neurons were classified as vertical semicircular canal related (n = 79, 71.2%) or otolith related (n = 25; 22.5%). Only seven neurons did not follow the usual response pattern and were classified as complex neurons. For the vertical canal-related neurons (n = 79) all eight major response vector orientations (ipsilateral or contralateral anterior canal, posterior canal, roll, and nose-down and nose-up pitch) were found in Fn on one side. Neurons with ipsilateral orientations were more numerous and on average more sensitive than those with contralateral orientations. Twenty-eight percent of the vertical canal-related neurons also responded to horizontal canal stimulation. None of the vertical canal-related neurons responded to static tilt. Otolith-related neurons (n = 25) had a phase relation close to head position and were considerably less numerous than canal-related neurons. Except for pitch, all other response vector orientations were found. Seventy percent of these neurons responding during dynamic stimulation also responded during static tilt. The sensitivity during dynamic stimulation was always higher than during static stimulation. Sixty-one percent of the otolith-related neurons responded also to horizontal canal stimulation. These results show that in FN, robust vestibular signals are abundant. Canal-related responses are much more common than otolith-related responses. Although for many canal neurons the responses can be related to single canal planes, convergence between vertical canals but also with horizontal canals is common.     

Coordinate frame for symmetry detection and object recognition.

Ss were required to determine whether dot patterns were symmetric. Cuing the Ss in advance about the orientation of the axis of symmetry produced a substantial speedup in performance (Exps 1 and 3) and an increase in accuracy with brief displays (Exp 2). The effects appeared roughly additive, with an overall advantage for vertical symmetry; thus, the vertical axis effect is not due to a tendency to prepare for the vertical axis. The cuing advantage was found to depend upon the S's knowing in advance the spatial location as well as orientation of the frame of reference (Exp 4). Exp 5 provided evidence that the frame of reference responsible for these effects is the same as the one that determines shape perception: Ss viewed displays containing a letter (at an unpredictable orientation) and a dot pattern, rapidly naming the letter and then determining whether the dots were symmetric about a prespecific axis. When the top–bottom axis of the letter was oriented the same way as the axis of symmetry for the dots, symmetry judgments were significantly more accurate. Results suggest a single frame of reference for both types of judgment. A theory of visual symmetry is proposed to account for the phenomena and characterize their relation to "mental rotation" effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial transformation of semicircular canal signals into abducens motor signals. A comparison between grass frogs and water frogs

The spatial transformation of semicircular canal signals to extraocular motor signals was studied by recording abducens nerve responses in grass and water frogs. Both species have similar vestibular canal coordinates but dissimilar orientations of their optic axes. Before sinusoidal oscillation in darkness the static head position was systematically altered to determine the planes of head oscillation in pitch and roll associated with minimal abducens nerve responses. Measured data and known canal plane vectors were used to calculate the abducens response vector in canal coordinates. The abducens vector deviated from the horizontal canal plane vector in grass frogs by 15 degrees and in water frogs by 34 degrees but was aligned with the pulling direction of the lateral rectus muscle in each of the two species. Lesion experiments demonstrated the importance of convergent inputs from the contralateral horizontal and anterior semicircular canals for the orientation of the abducens response vector. Thus, the orientation of the optic axis and the pulling directions of extraocular muscles are taken into account by the central organization of vestibulo-ocular reflexes. Horizontal and vertical canal signals are combined species-specifically to transform the spatial coordinates of sensory signals into appropriate extraocular motor signals.     

The stereoscopic anisotropy: Individual differences and underlying mechanisms.

Observers are more sensitive to variations in the depth of stereoscopic surfaces in a vertical than in a horizontal direction; however, there are large individual differences in this anisotropy. The authors measured discrimination thresholds for surfaces slanted about a vertical axis or inclined about a horizontal axis for 50 observers. Orientation and spatial frequency discrimination thresholds were also measured. For most observers, thresholds were lower for inclination than for slant and lower for orientation than for spatial frequency. There was a positive correlation between the 2 anisotropies, resulting from positive correlations between (a) orientation and inclination thresholds and (b) spatial frequency and slant thresholds. These results support the notion that surface inclination and slant perception is in part limited by the sensitivity of orientation and spatial frequency mechanisms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Tactile sensory anisotropy: Weber's contribution.

E. A. Essock, W. K. Krebs, and J. R. Prather (1997) found that detection of grid patterns by the fingers was best for longitudinal, then oblique, and, last, horizontal orientations. They suggested that the anisotropy is due to the number of cortical neurons tuned to a stimulus orientation. The contribution of E. H. Weber (1834/1996) deserves mention. He found that the 2-point threshold on the arm was lower for horizontal than for longitudinal orientations. He (1852/1965) explained this by elongated "sensory circles"—areas of skin served by single nerve fibers. The elongation followed the axis of the main sensory nerves (longitudinal in the arm). Horizontal acuity was finer because the stimulus interval covered more separate fibers. This account is similar to modern ideas on elongated receptive fields, although the locus is peripheral rather than central. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Postfusional latency in stereoscopic slant perception and the primitives of stereopsis.

Random dot stereograms of slanted surfaces were constructed, each representing one or two slanted surfaces in different relative arrangements and with different axes. Latency to fusion and from fusion to stereoscopic resolution was measured for each stimulus. It was found that latency to fusion was always very brief but that latency to stereoscopic resolution varied markedly, depending upon the orientation and arrangement of the stereoscopic surfaces. A gradient of discontinuities at a surface boundary produced an instant slant response for that surface, whereas a gradient of absolute disparities across the surface did not, except under conditions where vertical declination (a form of orientation disparity) was present. We conclude that stereopsis is not based on the primitives used in matching the images for fusion and that it is, at least initially, a response to disparity discontinuities which play no role in the fusion process. We also conclude that vertical declination is responded to globally as a slant around a horizontal axis but that other forms of orientation disparity are ineffective. The evidence from our experiments does not support the existence of a stereoscopic ability to respond globally to differences in magnification (or spatial frequency). It is suggested that stereoscopic perception of slant around a vertical axis is slow because it results from the integration of local processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Overrepresentation of horizontal and vertical orientation preferences in developing ferret area 17

One of the fundamental principles of visual cortical organization is that neurons form a "map" in which neighboring cells have similar orientation preferences. Previous anatomical and imaging studies have shown that although the exact layouts of these orientation preference maps vary between individuals, features of iso-orientation domains such as width and spacing appear constant within a species. Using chronic optical imaging of intrinsic signals we now demonstrate that in ferret area 17 a larger proportion of cortical surface is dominated by responses to horizontal and vertical contours than to the two oblique orientations. This was true for all ferrets studied both during development and in adulthood. Interestingly, however, we found that the degree of the overrepresentation varied significantly between individual animals. In some young ferrets, responses to horizontal and vertical stimuli developed faster than responses to oblique stimuli, and a much larger percentage of the cortex responded preferentially to horizontal and vertical stimuli. In other individuals, responses to all stimuli developed at roughly the same rate, and there was relatively little overrepresentation of horizontal and vertical preferences.     

Orientation of slit pupil and visual streak in the eye of the cat

The orientation of the visual streak of the cat's retina was compared to that of the long axis of the slit pupil in the same eye. In five paralyzed, anesthetized cats, the retinal projection to the superior colliculus was mapped with electrophysiological techniques. The orientation of the visual streak was estimated from the projection in visual space of the collicular region of high magnification which corresponds to the central projection of the streak. The angle by which the streak was tilted from absolute horizontal was always within one or two degree of the angle by which the pupil axis was tilted from absolute vertical. This relationship was confirmed in three of the animals in which small retinal lesions were placed a known distance from the histologically determined axis of the streak. From the visual coordinates of these lesions, an independent estimate of the streak's orientation was obtained. In each case, the tilt of streak axis from horizontal differed by no more than 0.5 degrees from the tilt of the pupil axis from vertical. The results support the hypothesis that planes containing the long axis of the cat's slit pupil are perpendicular to planes containing the long axis of the visual streak of the same eye.     

The orientation and direction selectivity of cells in macaque visual cortex

Quantitative data are presented on the orientation and direction specificity of the responses of cells in macaque monkey striate cortex. There is a bimodal distribution of direction-specific and nondirection-specific cells, with similar orientation tuning in each class. Cells range in orientation bandwidth at half amplitude from 6 degrees to 360 degrees (i.e. no orientation tuning), with a median near 40 degrees. Foveal-parafoveal and simple-complex subsamples show similar ranges of orientation bandwidths as well as similar medians (the bandwidths being somewhat broader than those found in cat cortex). The foveal subsample and a high-spatial-frequency subsample have more horizontal and vertical optimal orientations than oblique ones. Most cells show inhibition to some orientations, as well as excitation to others. Minimum-response orientations are generally less than 90 degrees from the optimal orientation--indicating maximum inhibition adjacent to the excitatory orientations. Three simple receptive field models are shown to differ in their abilities to account for these results.     

Cognitive coordinate systems: Accounts of mental rotation and individual differences in spatial ability.

Contends that strategic differences in spatial tasks can be explained in terms of different cognitive coordinate systems that Ss adopt. The strategy of mental rotation featured in many recent experiments uses a coordinate system defined by the standard axes of the human visual world (i.e., horizontal, vertical, and depth axes). Several other possible coordinate systems for solving the problems that occur in psychometric tests of spatial ability are examined. One alternative strategy uses a coordinate system defined by the demands of each test item, resulting in mental rotation around arbitrary, task-defined axes. Another strategy uses a coordinate system defined exclusively by the objects, producing representations invariant with the objects' orientation. Three experiments with 31 university students were conducted to assess differences in strategies used by Ss with high or low spatial ability in cube comparison and Shepard-Metzler (R. Shepard and J. Metzler; see record 1972-28060-001) rotation tasks. Two computer simulation models based on Ss' performance patterns are described. It is suggested that Ss high in spatial ability are faster in their manipulation processes and more flexible in adopting cognitive coordinate systems than their low-ability counterparts. (61 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Position and orientation features and the development of spatial concepts.

Tested the speed with which spatial information is classified into categories by asking 34 6-yr-olds, 35 10-yr-olds, 30 14-yr-olds, and 30 undergraduates to sort 6 decks of cards, each requiring a spatial judgment. Results indicate that (1) oblique discriminations required more processing time than did vertical–horizontal discriminations; (2) stimuli along the vertical axis were not processed significantly more quickly than stimuli along the horizontal axis; and (3) position variations slowed orientation discriminations, especially if the lines were of oblique orientation. The effect of position variations was particularly marked for the 6-yr-olds. The role of positional cues in spatial organization, as well as aspects of developmental changes in spatial concepts and strategies, are discussed. (French abstract) (11 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discrimination of shape reflections and shape orientations by Columba livia..

By using a free-operant instrumental discrimination procedure, it was demonstrated that pigeons find two-dimensional mirror-image visual forms more difficult to distinguish than otherwise similar forms. Variations in orientation of the discriminanda exacerbated the relative confusability of mirror images. No significant difference was found in the pigeons' performance whether the birds were discriminating vertically or horizontally reflected mirror-image pairs. Mirror images of shapes were also shown to be less discriminable than upside-down versions of shapes. The similarity of mirror-image patterns is discussed in relation to the generalized recognition of bilaterally symmetrical forms by pigeons. Pigeons found an orientation discrimination task involving a 45° tilt comparatively hard. A second experiment with a discrete-trial conditional paradigm confirmed that discriminations of shape orientations can be difficult for these birds. The addition of shape cues improved the performance on the orientation discrimination task, more so when arbitrary shapes were employed than when mirror images were used, which indicates again that the latter were more difficult to discriminate than the former. The relative insensitivity to shape orientations is ascribed to normal ecological demands on pigeons. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The determination of orientation relationships from the relative orientations of variants of a product phase

A method is given for determining orientation relationships from measurements of the orientations of variants of the product phase. The symmetry rotations relating the different variants are determined and the symmetry axes used to define the orientation of the parent crystal. Results are given for the orientation relationship between {111} annealing twins in a copper crystal and between Widmanstätten ferrite and austenite in an iron carbon alloy.     

The detection of bilateral symmetry: Effects of surrounding frames.

Examined whether the detection of bilateral symmetry in the fronto-parallel plane is influenced by surrounding frames. The study was conducted with 12 Ss. When obliquely or vertically oriented rectangular frames were presented simultaneously surrounding the dot patterns, the frames influenced symmetry detection. Vertical symmetry detection was slower in the tilted frame than it was in the vertical frame, and tilted symmetry was detected faster in the tilted frame than it was in the vertical. When there was a time delay between frame and pattern onset, there was no measurable frame effect. Symmetry detection was slowed when not in line with the long axis of the frame, whereas symmetry detection was not affected when the frame axis was aligned with the symmetry axis. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)