Perception

Two kinds of models have been proposed for taking into account the sensory processes at work in the detection of visual motion: the feature model and the frequency-filter model.

The problem of the complementarity of these models is raised. On the basis of empirical data, it is proposed that they are consistent.

In cats, responses of area 18 neurons to different moving patterns were measured. The influence of three movement parameters—direction, angular velocity, and amplitude of movement— were tested. The results indicate that in area 18 no ideal movement detector exists, but that simple and complex cells each perform complementary operations of primary visual areas, i.e. analysis and detection of movement.

The influence of deprivation procedures on the development of motion detection mechanisms has been studied in twenty-two kittens. Superior colliculus neurons did not acquire direction selectivity and normal ocular dominance in animals reared in the dark or in stroboscopic light. Neuron immaturity persisted in spite of a five week additional recovery period in normal conditions. Exposure to unidirectional visual motion for 10 h during the fifth week of postnatal age produced an asymmetric development of the two superior colliculi. Finally, unilateral neonatal ablation of visual cortex permanently impaired development of the ipsilateral superior colliculus. In the same or in different animals, development of optokinetic nystagmus, a typical visuomotor response, was similarly influenced by the global or selective deprivation procedures. These results suggest that motion detection mechanisms (both afferent and efferent) strongly depend upon constraints imposed by the visual world during the first weeks of life.

In the present work, we have shown the effect of a vestibular stimulation on the velocity perception of a moving scene. The intensity of this effect is related to the amplitude of the cart acceleration, image velocity, spatial frequency of the visual stimulus, and the angle between the directions of cart and image movement. A simple model has been developed to determine whether the perception of visual movement is due to the geometric projection of the vestibular evaluation on the visual vector, or the inverse.

The present experiments evaluated the effect of relative frequency as a determinant of the figure-ground organization of sequences of auditory tones. Observers counted sequences of 20 ms tones that were presented at the same frequency or that alternated between two different frequencies. The alternating tones differed in frequency by one whole tone, seven tones, or nineteen tones. Counting accuracy increased with increases in the silent interval between the tones. When the alternating tones differed by seven or nineteen tones, counting was disrupted at rates of presentation of eight tones per second or slower. In contrast to this decrement in the counting of tones that alternated by over an octave, very little decrement was observed when the tones alternated by just one whole tone. The best subjects counted these alternating tones more accurately than the tones presented at the same frequency. The poorest subjects showed a small decrement even when the tones alternated by just one whole tone. The results were discussed in terms of determinants of figure-ground organization in auditory information processing.

The occurrence of relatively long notes, and the repetition of melodic phrases are important cues to the metre, or regular beat, of a piece of music. A model of how people use this information to infer the metre of unaccompanied melodies is described here. The model is in the form of a computer program, and involves a definition of melodic repetition which encompasses repetitions that include certain kinds of variation. The program has been applied to the task of analysing the metric structure of the forty-eight fugue subjects of the Well-Tempered Clavier by J S Bach. The program is discussed in relation to other models both of musical understanding and of sequential concept learning.

Using simple, single angular figures, including figures containing only one line, we have shown systematic misestimations of distance defined by these figures. These misestimations are not related to the absolute distance per se, but are related both to the size of the angle defining the distance, and to the part of the angle defining it. Some implications of these findings are discussed.

The effects of orientation and spatial frequency of grating stimuli upon suppression were examined with a binocular rivalry paradigm in a group of ten strabismic patients and in a control normal group. Duration, frequency, and period of rivalry were examined as functions of differences in orientation and spatial frequency of dichoptic achromatic sinusoidal gratings. Records were made of responses by the sighting and by the nonsighting eye as well as responses during periods of combined binocular vision. Strabismic subjects reported normal binocular rivalry when presented with gratings of dissimilar orientation. Suppression of the deviating eye in strabismic subjects occurred with stimuli of similar orientation and was unaffected by spatial-frequency differences between dichoptic stimuli. Suppression was most intense under conditions that normally stimulate stereopsis and sensory fusion.

In an earlier study by Jansson and Johansson it was found that rotation of a rigid object is perceptually preferred over bending motion, and that bending motion in turn is preferred over two-dimensional stretching. The aim of the present experiment was to study if the same preference order is retained also when the proximal stimuli are changing in a physically more complex way. The stimuli were quadrangular outline figures with two stationary and two moving corners; the figures differed in degree of phase lag between the motions of the two corners. The result was that the preference order found earlier was retained. It was also found that the relative frequency of two subcategories of bending motion, bending proper and folding, varied with phase lag. The relation of the result to a principle of minimum object change was discussed.

A solid object—a frame enclosing rods—can be seen as having an illusory ‘line’ joining the tips of the rods.