Abstract: The perception of contrast was measured in humans by a technique of subjective contrast-matching, and was compared with contrast sensitivity as defined by threshold measures. 2. Contrast-matching between different spatial frequencies was performed correctly (especially at frequencies above 5 c/deg) despite the attenuation by optical and neural factors which cause large differences in contrast thresholds. 3. Contrast-matching between single lines of different widths was also veridical, and was not limited by the spatial integration (Ricco's Law) present at threshold. Adaptation to gratings altered the appearance of lines, and this could be best understood in Fourier terms. 4. The generality of these results was shown by matching the contrast of pictures which had been filtered so that each contained a one octave band of spatial frequencies. 5. Within the limits imposed by threshold and resolution, contrast-matching was largely independent of luminance and position on the retina. 6. Six out of eleven astigmatic observers showed considerable suprathreshold compensation for their orientation-specific neural deficit in contrast sensitivity. 7. These results define a new property of vision: contrast constancy. It is argued that spatial frequency channels in the visual cortex are organized to compensate for earlier attenuation. This achieves a dramatic 'deblurring' of the image, and optimizes the clarity of vision.

Abstract: The basic characteristics of the sensation of linear horizontal motion have been studied. Objective linear motion was induced by means of a moving cart. Visually induced linear motion perception (linearvection) was obtained by projection of moving images at the periphery of the visual field. Image velocity and luminance thresholds for the appearance of linearvection have been measured and are in the range of those for image motion detection (without sensation of self motion) by the visual system. Latencies of onset are around 1 sec and short term adaptation has been shown. The dynamic range of the visual analyser as judged by frequency analysis is lower than for the vestibular analyser. Conflicting situations in which visual cues contradict vestibular and other proprioceptive cues show, in the case of linearvection a dominance of vision which supports the idea of an essential although not independent role of vision in self motion perception.

Abstract: Hearing-impaired persons usually perceive speech by watching the face of the talker while listening through a hearing aid. Normal-hearing persons also tend to rely on visual cues, especially when they communicate in noisy or reverberant environments. Numerous clinical and laboratory studies on the auditory-visual performance of normal-hearing and hearing-impaired children and adults demonstrate that combined auditory-visual perception is superior to perception through either audition or vision alone. This paper reviews these studies and provides a rationale for routine evaluation of auditory-visual speech perception in audiology clinics.

Abstract: Metacontrast has been the subject of two neural network simulations by Weisstein and Bridgeman. We compare and elaborate on the two models, correct flaws not inherent in the models' conceptualizations, and discuss the remaining shortcomings. The idea behind how U-shaped metacontrast functions are generated is similar in both models, but the assumptions about how the visual system is organized are quite different. In one of the models temporal ringing, combined with a complex and implausible linking hypothesis, is necessary in order for masking to be obtained; this model assumes a single spatial and temporal channel. In the other model, masking does not depend on temporal ringing; this model assumes multiple spatial and temporal channels and a simple linking hypothesis. We show that of the two models only the second adequately predicts empirical metacontrast functions, and we relate this model to recent evidence that the visual system contains multiple channels. Sometimes treated as a puzzling and somewhat singular phenomenon, isolated from the \"mainstream\" of visual data and theory, metacontrast may, on the contrary, turn out to be one of the more interesting manifestations of a multiple-channel visual system.

Abstract: Human neonates selectively fixated patterns with curved rather than straight contours when the outermost contours differed in this form variable and when quantitative variables were controlled. The presence from birth of a discrimination ability basic to later form perception was evidenced.

Abstract: DONALD D. HAMMILL, Ed.D. Austin, Texas The relationship between certain visualperceptual abilities and school learning has long been a source of interest to educators, many of whom have speculated that deficits in visual perception may cause or, at least, contribute to academic failure. Historically, this assumption has been based upon the clinical experience of various members of the educational community as well as upon some basic research (Barrett, 1965; Bryan, 1964; Frostig & Maslow, 1969; Goins, 1958; Kephart, 1971; Pitcher-Baker, 1973; Rosen, 1966; Wepman, 1964). While visual perception and, in particular, its relationship to school learning have received much attention in professional journals, the educational usefulness of this important theoretical construct has never been fully substantiated. In fact, recent opinion and research have seriously questioned its relevance as a practical correlate of learning failure (Cohen, 1969; Hammill, 1972; Mann, 1970). It is important to note, however, that many school systems throughout the country are still committing large numbers of man hours

Abstract: It is often that the spatial senses (vision, hearing and the tactual senses) operate as distinct and independent modalities and, moreover, that vision is crucial to the development of spatial abilities. However, well controlled studies of blind persons with adequate experience show that they can function usefully in space. In other words, vision is not a necessary condition for spatial awareness. On the other hand, thought the blind may be equal or even superior to the sighted when performing spatial tasks within the body space, they may be deficient, either developmentally or absolutely, in tasks which involve events at a distance from the body, principally in auditory localization. One possible explanation of the differences between blind and sighted (McKinney, 1964; Attneave & Benson, 1969, Warren, 1970) is that vision is the primary spatial reference, and inputs from other modalities are fitted to a visual map. Several criticisms of this theory are adduced and an alternative theory derived from Sherrington (1947), in which all sensory inputs map on to efferent patterns, is sketched.

Abstract: 1. Lesions were made in cortical Area 17 (Visual I) of eight cats which were then allowed to recover. 2. During acute experiments between 1 and 11 weeks after the lesion the activity of Area 18 (Visual II) units was recorded and the results were compared with those obtained in normal cats. 3. The receptive fields were similar in size and distribution in the two groups but the lesioned animals had a much higher proportion of units unaffected by a visual stimulus and a higher proportion of the visually responsive units lacked specific direction or orientation preference. 4. Of six units which were tested in Area 18 of cats with lesions five showed variability of their direction or orientation preference with time. 5. The effects described above are most probably due to destruction of the corticocortical pathway which connects Areas 17 and 18. Some units in Area 18 appear to be driven by visual stimuli via their geniculate input alone. The corticocortical (Area 17 to 18) pathway may normally confer additional specificity on some of these units.

Abstract: THE human retina projects not only to the lateral geniculate bodies and from there to the visual cortices, but in a parallel fashion to several other subcortical centres as well. One such centre is the superior colliculus, and it has been suggested that a rudimentary discrimination capacity of the locus of visual stimuli may be mediated by this structure1. Results of anatomical studies with subhuman primates indicate that the macular region does not project to the superior colliculus2,3 (or that it is represented by a different population of retinal fibres which have not yet been identified by anatomical techniques4). The macular region seems to project only to the lateral geniculate bodies and from there to visual cortices, whereas the retinal periphery projects to several subcortical centres. This raises the question of whether a similar dissociation of projection between the central and peripheral retina also can be found in the human visual system. We present data obtained from patients with lesions of the central visual pathways which indeed suggest such a dissociation.

Abstract: Apparatus and methods for testing temporal resolution of vision in a human subject are disclosed in which a light source is repetitively energized to produce pairs of visual stimuli, and the time interval between two stimuli in each pair is varied so as to enable the assessment of the minimum interval for which the subject under test can discern the separate stimuli in the pair. Means are provided for fixating the center of the subject's visual field, and the position of the visual stimuli within the visual field is varied so as to enable a map to be drawn showing the variation of the subject's temporal resolution over his visual field. Temporal resolution measured in this way enables certain diseases to be diagnosed and distinguished.

Abstract: Verbal descriptions, photographs and maps are reviewed for the kind of selective information they impart (§1). The need is established for a critical analysis of the assumption that we can not only map the invariant features of the physical world but also represent the optical world, the changing appearance of objects as it is conveyed to the camera and to the eye by reflected light. As long as this light was identified with the stimulus pattern causing visual sensations it could be assumed that appearances were uniquely determined and could thus be uniquely represented, but this view conflicts with the insight that there are many other variables influencing our visual experience. Visual sensations as such cannot be isolated by introspection but they can be aroused and manipulated by artifice based on the knowledge of the physiology and psychology of visual perception (painting, stereoscope, film, television). The surprise caused by such unexpected visual effects underlies the notion of illusion. Artistic experiments in registering and arousing visual sensations are discussed (§ 2). These experiments show the need to give subjectivism its due without falling into the trap of complete relativism. It is here that the consideration of maps and mapping styles is helpful. The keys and symbols adopted by map makers suggest that visual conventions can but need not rest on arbitrary choice and are rarely devoid of psychological effects. These effects, however, are independent of the truth or falsehood of the information compiled by surveying instruments of any kind. It is possible to predict what aspect of a physical array will be visible from any given point in space (§ 3). The theory underlying this prediction is that of central perspective based on the ‘visual cone’. The procedure is not reversible, the information imparted by a perspectival representation does not uniquely determine the object represented. This multivalence of monocular stationary vision (the tracing on the window pane) has given rise to many psychological puzzles concerning the determinants of appearances such as the constancy phenomena (§ 5). More recently J. J. Gibson has challenged the relevance of these puzzles and experiments and emphasized the resources afforded by the ambient light for the veridical perception by a moving organism of the invariant environment. This challenge has created a fresh problem for the theory of pictorial representation (including photographs) and made it more urgent to investigate the visual experience aroused by such representations in varying conditions (§5). A comparison between the information conveyed by pictorial representations and the information picked up by the eye inspecting a real scene may provide opportunities for testing Gibson’s account and help to clarify the limits of veridical perception. Probing reactions to distant prospects in reality, paintings or photographs may reveal that the experienced stability of their appearance can be upset. Even the clouds in the sky and the vault of heaven are subject to various perceptual interpretations which rarely impinge on our awareness. Far from justifying a representational relativism these variations confirm the need for an anchorage of representation in the objective procedures of perspective (§6). It is suggested that the indeterminacy of visual interpretation disposes of the time-honoured problem of the apparent curvature of the phenomenal world. Demands for an alternative system of perspectival representation which appeal to this experience rest on a confusion between the mirror and the map. We can map the physical world but not its variable and shifting appearance. This conclusion, however, is not intended to discourage artistic attempts to record a visual experience. On the contrary: all experiments on the hoardings, on the screen and in paintings probing our cognitive and emotional response to images should be of interest to the student of human reactions (§7).