From the phenomenological standpoint, the world of experience consists of perceivable things and events that display as many qualities, relations, states and changes as there are modes of appearances in Katz’s sense, of which movement has been the object of many phenomenological studies (see the classical Duncker, 1929; Oppenheimer, 1935). Brown’s work is devoted to the properties of velocity and time in perceived movement. It is also another example of the fact that criticism of the constancy hypothesis as well as the stimulus error does not imply the rejection of physical knowledge for a careful design of the stimulation to discover the self-sufficient factors of perception.
Brown (1930a, b) maintains that the explanations and even the data of earlier research into the perception of velocity are not satisfying because they assume that the real world is reducible to the object of investigation of physics and that psychological phenomena are only epiphenomena. It is taken for granted that there is only one correct value of the perceived velocity, namely the one that corresponds to the velocity of the stimulus in given experimental conditions. The values that diverge from it are explained away as illusions or errors of judgement. Yet Brown makes reference to the physical definition of velocity by the equation v = s/t to design the experimental conditions in which clear-cut phenomena can be brought about to analyze the phenomenological factors of the perception of velocity. In opposition to the constancy hypothesis, he shows that the perception of velocity is determined by a multiplicity of factors regarding the structure of the field where the movement occurs, while perceived velocity equals that of stimuli only if all these factors are kept constant.
For the research into the perception of velocity, Brown constructs two fields in which objects are seen moving through a diaphragm at adjustable speeds, whose distance from subjects, size and surrounding structure can be controlled. Subjects are asked to adjust the velocity of objects in one field to match the perceived velocity in the other field under varying conditions. Having designated the fields with “A” and “B,” the difference in the phenomenal velocities is expressed by the ratio Va/Vb. Therefore, this ratio tells which physical velocity of the objects in two different fields is needed for the objects to appear to move at equal phenomenal velocity. Indeed, Vb is how much B’s velocity is contained in A for the same apparent velocity to obtain. For example, the ratio 1.20 means that for equal physical velocities B appears to move faster than A by 20 per cent, so that A’s velocity is to be increased by 20 per cent or conversely B’s is to be decreased by 20 per cent for the phenomenal equality of velocity to ensue. Hence, Va/Vb = 1 means that both stimulus and phenomenal velocities of A and B are identical. Brown reasons that if the phenomenal velocity can be equated to the quotient s/t, space could be measured either as the retinal space that is traversed by the stimulus or as the phenomenal space. If the velocity of an object moving at a 2 m distance is perceived with a stationary eye, since v = s/t if s doubles with t held constant, then the retinal velocity should also double. Yet, ordinary experience shows that perceptual velocity is constant: if, for instance, a car is seen moving at 10 m and then at 20 m, no change of apparent velocity is detected. If a field in which objects move at a 10 cm/sec. constant velocity is placed at distances varying from 3.3 m to 10 m, while another field is kept at a 1 m distance, the Va/Vb ratio ranges from 1 to 1.25 while the retinal velocities vary from 1 to 10.
As regards phenomenal space, Brown reports an experiment with fields of constant apparent size, which are placed at distances between 1 m and 10 m, where phenomenal velocities sensibly decrease at increasing distances from the subjects. Brown states that in effect a relative constancy of velocity is found at increasing distances, but also that it cannot be deduced from the visual size constancy because the values of the former are not as constant as expected were they dependent upon the latter. Instead, if subjects are asked to compare the velocities of two fields respectively at 4 m and 2 m, whose diaphragms, objects size and intervals are in a 1:2 ratio, Vb almost doubles Va. If both fields are placed at a 2 m distance from the subjects, the velocity ratio remains the same. Given the above-mentioned findings for the retinal projection, the visual size of objects and their intermediate spaces, Brown concludes that, all other conditions being equal, the first factor that accounts for the perception of velocity is the size of the visual field where the movement occurs.
Brown found that with homogeneous fields, if B is smaller by half than A in all respects, the objects in B are to be adjusted to move at half the velocity of the objects seen in A for the velocities to appear the same. In general, at equal physical velocities smaller fields present objects that appear to move faster than the objects of greater fields. Brown (1930a: 211, 226) concludes that for a transformation of linear dimensions between A and B, the velocity must be transformed the same amount to appear equal. In fact, this relation holds for homogeneous fields. If A’s and B’s linear dimensions have a 2:1 relation and are presented so that the illumination makes visible first the fields in a dim light, then only some contours thereof, and finally makes them nearly homogeneous, then the Va/Vb ratio averages respectively 1.76, 1.87, 1.98. When the decrease in homogeneity is controlled in terms of an increase in the visible structure that surrounds the fields of movement, the evidence is obtained that it is another factor of the perception of velocity (1930a: 218). For example, the Va/Vb ratio increases as the amount of a wallpaper made up of small squares covering the fields is greater for B than for A. If A and B are equal in all respects except that A has a homogeneous surrounding while B is covered by the wallpaper, then Va on average has to be increased by 25 per cent to appear equal to average Vb, since B’s objects appear to move faster. This agrees with the finding that less homogeneity implies lower thresholds for the perception of movement and higher phenomenal velocities (Brown, 1930c).
As Koffka (1955) remarks, Brown’s theory is confirmed by observing that if only some dimensions of the field are changed while all the others are kept constant, even with various combinations of length, width and size values the change of phenomenal velocity is less than what is obtained through a transformation of all dimensions. For fields in a 2:1 size ratio, if the objects are of constant size the Va/Vb ratio is 1.38 instead of 2. For fields of the same size with objects of varying sizes, Va = Vb if the larger objects move faster than the smaller ones. For equal physical velocity, increasing the object’s size decreases the phenomenal velocity. Brown (1930a, 221) remarks that these results regard the size of perceptual objects. It is indeed the size of what appears as figure, rather than the absolute size, that influences the perception of velocity. If A presents two lines that are so far apart that they are seen as two segregated lines, while B presents two lines that are so close that they are seen as a figure, the Va/Vb ratio is always greater than one.
Brown (1930b) resorts to the same reasoning in order to define the experimental problem and the constructs to investigate the phenomenological factors of time perception. Brown considers that for any factor of the perception of velocity, if the phenomenal space varies proportionally to the physical space of the stimulus device, the increase of apparent velocity implies a decrease of the phenomenal time. This reasoning is valid if the physical equation of velocity holds also for phenomenal quantities. For Va/Vb = 1.20, the equation holds: Va < Vb = (Sa/Ta) < (SbTb). Since physical and phenomenal quantities denoted by “S” are held constant for a given factor of the perception of velocity, the Ta/ Tb ratio for phenomenal times has to be 1.20, that is to say it is hypothesized that time appears somehow to flow faster in B than in A for equal spaces in both fields.[1] To test this hypothesis, Brown asked subjects to adjust the velocity of objects in A until they move across the field in a time that appears equal to a standard interval between two successive lights or buzzes, which is held constant by the experimenter. Then subjects had to repeat this task for B. The physical times of A, B and the standard interval provide the data to build the conditions in which the equality of time is perceived in the different fields. The Ta/Tb ratio is predicted from the Va/Vb ratio, so that the quantity by which the time of A and B has to be altered for a given factor that characterizes either field is easily computed and then confronted with the observed values. For instance, at equal physical velocities the 1.20 velocity ratio means by hypothesis that the temporal stretch of the movement in B appears shorter than in A to cover equal phenomenal spaces. Hence, it can be controlled that as A should have increased its apparent velocity to match B, so either the physical time of movement in A should be shortened or the physical time of movement in B should be lengthened for both A and B to match the standard temporal interval. Since Brown finds a good agreement between predicted and observed values, he draws the conclusion that time perception depends on the visual structures of the field. For every factor of the field structure that accounts for the perception of velocity, the variation of phenomenal velocity occurs for an inverse variation by a corresponding amount of phenomenal time for equal spaces.
Source: Calì Carmelo (2017), Phenomenology of Perception: Theories and Experimental Evidence, Brill.
11 Aug 2021
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11 Aug 2021
10 Aug 2021
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11 Aug 2021