Perception

The subjects listened to one of two simultaneous synthetic speech syllables delivered independently over two loudspeakers. When the loudspeakers were situated at 90° to the left and to the right, right-side advantage was found. When one loudspeaker was situated in front of the subject in the median plane, and the other at one of several azimuthal positions around him, an advantage of the frontal position was observed in all cases. On the other hand, performance on the nonfrontal message was affected significantly by its position. The pattern of performance which is observed can be described in terms of three component factors: a right-side advantage, related presumably to cerebral dominance, an advantage of sources situated in front of the subject over those at his back, and possibly an advantage of sources near the median plane over more remote ones.

Luneburg's model for computation of the curvature K of visual two-dimensional space (horizontal visual surface) was tested with equidistant and parallel alleys in large open spaces. Forty-six subjects used stakes to produce 406 experimental alleys of variable sizes (from 5 × 1 to 240 m × 48 m). The results show that, contrary to results obtained under laboratory conditions with small alleys and light spots, the individual curvature of visual space does not have a negative constant value. K varies in the interval −1 to +1 in ninety computed settings: K ≥ 0 (N = 38); K < 0 (N = 52). Therefore the Lobachevskian geometry currently attributed to visual space ought to be replaced by a Riemannian geometry of variable curvature. Moreover K is an individual function dependant on the size of the alley (distance from the subject), and visual perception would be better understood as scale-dependent. Independently of Luneburg's model we have tested the constancy of the curvature hypothesis in experiments with horopters and visual triangles. The results obtained invalidate Luneburg's hypothesis also.

Five groups of five-month-old infants observed the same horizontal arrangement of a three-element stimulus placed in a rectangular frame during a series of habituating trials. These trials were followed by either (i) additional exposure to the familiarized standard, (ii) a triangular rearrangement of the three stimulus elements, (iii) oblique rotation of the three elements, (iv) oblique rotation of the three elements and the frame, or (v) oblique rotation of the frame alone. The infants were responsive to all changes in the spatial arrangement of the three elements and to the rotation of the frame, but were less responsive to the change in the frame. The two effects were not additive.

The ability to make discriminations of binocular disparity was investigated in 2-month-old infants by two methods: (a) fixation preference between patterns differing in the disparity they contained, and (b) recovery from habituation of high-amplitude sucking when there was a change in disparity in the visual reinforcer. The stimuli were random-dot stereograms. The results for both methods indicated that at least some infants of this age could perform stereoscopic discriminations and that both techniques were feasible for development for longitudinal studies of stereoscopic vision.

The ability to reproduce two-dimensional and three-dimensional spatial models was tested in eighteen blind children, aged seven to eleven with two tasks (block design test and stick test). Performances and strategies were compared with those of seeing children. The results failed to show any important specific errors in blind children; despite blindness some children reached levels of performance as good as those of seeing children, while others completely failed to follow instructions. All such effects were independent of age. The problem is raised of the psychological conditions of space representation, independent of the afferences through which space is perceived.

In an experiment on perceptual learning, monkeys were given the opportunity to watch on television the ‘private behaviour’ of another monkey (which did not know it was being watched). The subjects were shown monkey X for twenty sessions in a row, followed by monkey Y for twenty sessions, followed by monkey X again for twenty sessions. The subjects' ‘interest’ in the stimulus monkey remained roughly level within each block of twenty sessions, but increased in a step-like way at the changeover from X to Y, and again from Y to X. These results are interpreted as evidence that the subjects gained little or no extra insight into the nature of private behaviour through watching the same monkey in successive sessions; the critical factor in their perceptual education was the comparison between one monkey's behaviour and another's.

Pigeons learned to discriminate between ‘A’s and ‘2’s in eighteen different typefaces. They subsequently showed excellent transfer to twenty-two typefaces that they had not previously seen; one pigeon was tested with handwritten letters and responded correctly to them also. Pigeons' responses to ‘A’s and ‘2’s with parts removed suggested that their performance was controlled by several features, none of which alone could be considered necessary or sufficient. A test in which birds were shown other letters of the alphabet supported this conclusion. It appears that the original discrimination was learned as what Ryle calls a ‘polymorphous concept’.

Random-dot Moiré patterns are manipulated to destroy our ability to perceive the spatial correlations which remain present in the patterns.

Two experiments show that the young child copies or places diamond and square shapes in alignment with the surrounding frame. The results are related to the difficulty exhibited by young children in drawing diamonds versus squares.

Pairs of geometric forms of equal area were presented, one form after another, with interstimulus intervals t ranging from 0 to 250 ms. The subject's task in experiment 1 was to recognise both stimuli. Identification of the form presented first (backward masking) across all values of t was of a nonmonotonic nature, with greatest impairment at values of t from 30 to 60 ms. Identification of the second form presented (forward masking) increased monotonically with increasing t. Different forms were recognised with different effectiveness across all values of t where masking took place. The results are interpreted on the basis of a multiple-stage processing model which assumes interaction between stimuli at different levels at different values of t. In experiment 2 the subject's task was to detect the presence or absence of a predesignated form. This condition yielded monotonic functions for both backward and forward masking. An explanation in terms of attention-dependent masking is given.

After inspection of vertical sinusoidal gratings at least three distinct types of subjective or ‘hallucinated’ patterns can be seen on a uniform test field. One type, here called horizontal streaming (H), is already well-known from the work of MacKay. A second type (V) looks like a roughly sinusoidal grating about 15 octaves above the adapting spatial frequency. Under optimal conditions a second vertical component appears at about 2 octaves below the adapting frequency. The third category of aftereffect consists of diagonal lines (D) at two orientations (about ±40° from vertical). The spatial-frequency band at these two orientations appears to be fairly broad, but roughly similar to the adapting frequency. The duration and strength of D increased, while V declined, at higher adapting spatial frequencies. D and V were increasing functions of adapting contrast, while H appeared abruptly only after the highest adapting contrast. H, D, and V are thus all functionally distinct.

A schematic model of cortical organization is proposed to account for these phenomena. Pattern channels selective for a given orientation are grouped together with movement channels selective for the orthogonal direction. Antagonism between channels within such ‘modules’ accounts for the streaming effect (H). Inhibition between modules tuned to different orientations and spatial frequencies accounts for the D and V effects: after adaptation of channels in one module, neighbouring module(s) are released from inhibition to produce a spurious response which is seen as a grating-like object in the adapted part of the visual field. During flickering adaptation a ‘hallucinated’ lattice can be seen superimposed on the adapting grating. It apparently consists of Fourier components more remote from the adapting pattern than D and V are. This disinhibitory effect is strong confirmation of the inhibitory model. The regular and highly organized matrix of channels implied by these experiments may constitute a cortical hypercolumn conducting a coarse, piecewise Fourier transformation of the retinal image.

The duration of the movement aftereffect was measured in twenty-four normally binocular subjects and in eighteen subjects who lacked stereopsis as a consequence of childhood strabismus. Aftereffects were generated monocularly and binocularly, and compared to those which occurred after adaptation of one eye and testing with the other. Normal subjects were categorized on two indices of eye dominance, which involved sighting and rivalry tests. The monocular-aftereffect durations were slightly longer when the dominant eye was used, and interocular transfer from the dominant eye to the nondominant eye was greater than the transfer in the reverse direction; however, these differences were not statistically significant. The results from the strabismic subjects suggested that they fell into two distinct groups: one group (seven of the eighteen subjects) experienced no interocular transfer in either direction; the other group did yield some interocular transfer, and it was generally greater after adaptation of the dominant eye and testing the nondominant eye than in the reverse direction. Six of the seven subjects who failed to show any transfer still had misalignment of the visual axes, but this was not the case in any of the subjects exhibiting transfer.