Constancy Mechanisms Research Articles

Perceived distance and the perceived speed of self-motion: Linear vs. angular velocity?

Experiments are reported in which it was found that, with the angular speed of a visual surround held constant, the perceived speed of rotary self-motion increased linearly with increasing perceived distance of this surround. This finding was in agreement with a motion constancy equation derived from a consideration of object-referred motion perception. Since information concerning distance is necessary for the perception of linear but not angular speed, this finding supports the conclusion that visually perceived rotary self-motion perception is dependent upon perceived linear surround motion at least in the horizontal plane. The visual motion constancy mechanism which operates for object-referred motion can apparently not be switched off for the special case of self-motion perception.

Physiological mechanisms of color constancy

Color constancy is the term given to the ability to recognize the color of objects correctly under different conditions of illumination. For this purpose the visual system must determine the character of the illumination, introduce a correction for it into the spectal composition of the light received from the object, and hence recreate the true color of its surface. Behavioral experiments on fish showed that they possess constant color vision of objects. Electrophysiological experiments on ganglion cells of the color type showed that the simplest mechanisms of correction for illumination are found at the retinal level. An investigation of model algorithms providing for color constancy showed thatthe presence of color vision makes it much easier to recognize the three-dimensional form of objects. This fact compels a reexamination of established views regarding the place and role of color vision in functions of the animal visual system as a whole.

Torsional eye movements and constancy of the visual field

The eye movements during lateral head tilting were investigated. For recording the eye movements we used Yarbus' method of the suction device. It is found that the smooth tilts of the head to the shoulder cause two kinds of the eye movements. The first is a slow rotation of the eye in the direction opposite to one of the head. During this phase the attitude of the eye with reference to the gravity vertical is not altering. The second kind of the eye movement is a saccadic rotation about the visual axis in the direction of the head tilt. The speed of these saccades is about 200°/sec. The sizes of the saccades are in the 0.5–8° range. The two described types of eye rotations correspond to the mechanisms of the orientation constancy in the visual system. In the slow phase the constancy is provided by keeping the eye attitude unchanged. But during the fast phase the saccades change the eye orientation in space and the action of a neuronal mechanism is supposed. This mechanism is to transform the retinae afferentation some proper way. From this point of view the results of the near electrophisiological studies of the constant elements in the visual cortex of unaesthetized cats are cleared.

What Variables Produce Similarity Grouping?

The effectiveness of several configurational or textural variables in producing similarity grouping was investigated by measuring the time it took Ss to locate the disparate quadrant in a circular array. The 'figure' and 'ground' quadrants differed in (1) slope of elements, (2) linearity of elements, or (3) the way in which the same slopes were combined into angles. Differences in slope produced excellent grouping; differences in linearity were less effective; and differences in arrangement of slopes were generally quite ineffective. Grouping was also dependent on orientation of the whole array: horizontals and verticals gave better grouping than diagonals, and even arrangement of slopes gave moderately effective grouping when angles with horizontal and vertical axes of symmetry were opposed to each other. Conditions of head tilt were used to determine whether the grouping effects were dependent on retinal or gravitational orientation. For the angles, only retinal orientation seemed important; but for line segments and paired dots varying in slope, both retinal and gravitational orientation had significant effects. The results disconfirm the hypothesis that grouping occurs entirely on a projection level, independently of constancy mechanisms. It is suggested that grouping and segregation depend on identities and differences between descriptors which in turn represent relationships between the stimulus array and an internal Cartesian reference system. Similarity is one of the most important of Wertheimer's principles of perceptual grouping, but only recently, with the work of Julesz and Beck, has any appreciable curiosity been displayed about the kinds of similarity that are effective in this respect.' It should, of course, be understood that grouping always implies the complementary process of segregation. Grouped items must be at once similar to one another and different from extraneous items; in analysis-of-variance terminology, within-group variance must be Received for publication September 22, 1969. The research was supported in part by the Air Force Office of Scientific Research (Grant 973-66) and in part by the Advanced Research Projects Agency of the Department of Defense (Contract F44620-67C-0099). 1 M. Wertheimer, Untersuchungen zur Lehre von der Gestalt, Psychol. Forsch., 4, 1923, 301-350; B. Julesz, Texture and visual perception, Sci. Amer., 212, 1965, 38-48; J. Beck, Perceptual grouping produced by line figures, Percept. & Psychophys., 2, 1967, 491-495.

Intensity-volume interaction effects in gustatory perception

Three paired comparison type experiments, with 20 different Ss in each, using citric acid at three concentration levels as taste stimulus, investigated some effects of differences in stimulus liquid bulk on perceived relative taste intensity, and effects of concentration differences on perceived relative volume. Perceived relative taste intensity increases slightly with increasing liquid bulk and relative perceived bulk increases slightly with concentration, both effects being significant: p < .01. An explanation in terms of a taste-quantity constancy mechanism is advanced.