Hock, Howard S.

Ullman (1979) has proposed a measurement metric, which he termed “affinity." He described affinity as a certain similarity measure between successively presented surfaces as it affects the perception of apparent motion between the surfaces. Later, the concept of “affinity” has been extended; it entails that how the perception of motion within a surface is affected by its grouping strength with adjacent surfaces (Hock and Nichols, 2012). It has been found that the more attributes, that are shared by the adjacent surfaces, the greater the likelihood of their being grouped together. However, Ullman (1979) suggested that the relative affinities of pairs of surfaces could determine the solutions for the motion correspondence problem (when more than one motion path is possible). However, it has remained unknown whether the effects of affinity on solutions to the correspondence problem are due to its effects on a single surface apparent motion strength or pre-selection biases; i.e., the top-down effects of perceptual grouping favoring the perception of motion in one direction as opposed to other competing directions. In the current study, it has been confirmed that motion within a surface is affected by its affinity with adjacent surfaces. The current study also confirmed that affinity has a small, but significant effect on motion strength when motion surfaces are presented in a single surface apparent motion configuration, evidence for top-down effects in which motion strength can be affected by affinity. In motion correspondence problem, affinity affects the perceived motion direction due to competition is consistent with the solution to the motion correspondence problem being affected by the relative affinity-determined strength of competing motion signals. But it is seen that there is strong affinity is due to preselection identity biases. To conclude, in motion correspondence problem, stronger motion is perceived between the two similar surfaces is due to pre-selection biases resulting from the perceptual grouping of surfaces with the greatest affinity; i.e., the top-down effects favoring the perception of motion in one direction as opposed to other competing directions.

Objects in a scene are likely to occlude other objects partially and are itself likely
to be partially occluded. A central question, therefore, is how the visual system resolves
the resulting surface correspondence problem by successfully determining which surfaces
belong to which objects. To this end, a recently developed dynamic grouping
methodology has determined whether pairs of adjacent surfaces are grouped (Hock &
Nichols, 2012). The grouping of adjacent surfaces, which depends on their affinity state,
is indicated by the direction of perceived motion across one surface when its luminance is
perturbed. In the current stimuli, which consists of a horizontal surface partially occluded
by a vertical bar, dynamic grouping also can occur for nonadjacent surfaces, providing
they are linked in two-dimensions by a connecting surface. Results indicate that the
dynamic grouping motion is stronger for amodal completion entailing the perceptual
grouping of nonadjacent surfaces behind an occluder.

Prior research has explored the counterchange model of motion detection in terms of counterchanging information that originates in the stimulus foreground (or objects). These experiments explore counterchange apparent motion with regard to a new apparent motion stimulus where the necessary counterchanging information required for apparent motion is provided by altering the luminance of the background. It was found that apparent motion produced by background-counterchange requires longer frame durations and lower levels of average stimulus contrast compared to foreground-counterchange. Furthermore, inter-object distance does not influence apparent motion produced by background-counterchange to the degree it influences apparent motion produced by foreground-counterchange.

The effects of the onset, offset, and sustained presence of inducing lines on the perceived position of test lines were independently investigated in a vernier alignment task. For spatial separations larger than 2.3 min, repulsion effects were always observed. For the smallest spatial separation, 2.3 min, the effect of the inducing lines was attraction for 0 and 195 SOAs. Minimal attraction was observed for a 3000 SOA. However, when the offset effect was isolated using the 3000 SOA and a 0 ISI, a large repulsion effect was observed for the 2.3 min spatial separation, as well as for the larger spatial separations. These results indicate that the temporal separation between visual elements is as important in determining perceived position as their spatial separation, which has been demonstrated in earlier studies (Badcock & Westheimer, 1985). A differential gradient model is proposed which accounts for these findings in terms of excitatory and inhibitory interactions within an ensemble of position-sensitive units.

The effects of adaptation on motion were investigated using a modified apparent motion display. Unlike the classical apparent motion display, a BRLC (background relative luminance contrast) apparent motion display consists of two visible dots, each of a different luminance, which remain in the same position but exchange luminances on successive frames. This forms a bistable stimulus; stationarity-flicker or motion may be perceived, depending on the value of the BRLC. There was a significant interaction between condition (baseline or adaptation) and BRLC when testing motion perception following adaptation to a moving stimulus, a flickering stimulus and a static stimulus. Additionally, adaptation to flicker decreased motion perception at high BRLC values and increased it at low BRLC values. Our results reflected the presence of strong inhibitory competition between the mechanisms concerned with the perception of motion and stationarity which restricted adaptation effects to certain values of BRLC.

The aim of this project was to clarify the findings of Shapiro and Levine (1990) by exploring post-verb argument structure complexity effects. Three verb types, transitives, datives and obligatory three-place, were probed at four positions during an on-line sentence processing task that utilized cross-modal naming as the secondary task in a reaction time paradigm. No significant verb x probe interaction was found at any probe position with any of the three verb types. Two possible explanations are given for this pattern of results: (1) the choice of cross-modal naming as the secondary task; and, (2) the high variability of reaction times among subjects.

Anstis, et al. (1985) have reported that under certain conditions the visual system adapts and the perception of apparent motion breaks down. The present research indicates that breakdown is actually a result of same-place mechanisms successfully competing with motion-detecting mechanisms. Thus, the perception of stationarity (with flicker) can occur at the start of a trial and spontaneously switch to the perception of motion, or vice versa. The response of same-place mechanisms depends on the zero-hertz energy at each location of an apparent motion stimulus, whereas the response of motion mechanisms depends on the time-varying energy. Average luminance, luminance contrast, the temporal symmetry of the apparent motion display, and relative phase are manipulated to investigate competition between same-place and motion-detecting mechanisms.

Subjects judge motion direction for an apparent motion stimulus with competing perceptual organizations: Vertical vs. horizontal motion. The two patterns are coupled. When one is perceptually instantiated the other remains active in memory, resulting in sudden changes in perceived motion direction under constant stimulus conditions. The probability of change from an initially horizontal to a vertical pattern remains constant over time, showing that perceptual satiation is insufficient to explain the occurrence of spontaneous perceptual changes. It is proposed that spontaneous changes also occur because the pattern active in memory attracts the percept away from the currently instantiated pattern. The attraction hypothesis specifies that the activation of the memory pattern (and hence its attractive strength) increases as a result of previous experience. It is supported by evidence that the likelihood of changing, say from horizontal to vertical motion, is increased if the motion pattern was previously vertical.

A row of dots is presented in a series of alternating frames; dots in each frame are located at the midpoints between dots of the preceding frame. Although the perceived frame-to-frame direction of motion could vary randomly, cooperativity is indicated by the emergence of two coherent motion patterns, one unidirectional, the other oscillatory. Small increases in the time between frames are sufficient for the bias, which maintains the previously established motion direction (unidirectional motion), to be reversed, becoming a bias which inhibits that direction (oscillatory motion). Unidirectional motion, which predominates for small dot separations, and oscillatory motion, which predominates for large separations, are associated with short-range and long-range motion (Braddick, 1974) by manipulating the shape of the dots, their luminance, and the luminance of the inter-frame blank field. Pulsing/flicker emerges as a third perceptual state that competes with unidirectional motion for very small dot separations.

Six experiments were performed to examine the adequacy of detection/computation models for understanding the perception of relational motion, and in particular, the perception of three-dimensional motion in two-dimensional displays. The stimuli were a pair of dots which moved relationally (i.e., the relative location of the dots changed). Three-dimensional motion was seen when a contraction of the stimulus preceded an expansion (i.e., the dot separation first decreased, then increased), the angular difference between the pattern orientation and the direction of movement was small, and the spatial separation between dots was small. Neither the activation of higher-order, relational feature detectors, nor the construction/computation of relational motion from the detected motion of individual dots, can adequately explain the perception of three-dimensional motion.