Irvin Rock

The effect of inattention on form perception.

A state of inattention was achieved by having subjects selectively attend to one of two overlapping novel figures in a series of such overlapping figures. Recognition of form directly afterward was good for figures that had been attended to but was essentially nil for the unattended figures. Recognition failed to occur even if a familiar figure was in the unattended series and even if that figure was presented 1 sec before the test. A further experiment showed that certain general characteristics of the unattended figures other than form were recognized. The results are interpreted as indicating that attention is necessary for form perception, not merely for memory of form. It is suggested that a cognitive process of description constitutes the essence of form perception. Diverting attention eliminates the cognitive operation of describing the spatial relations that characterize a figure.

A case of viewer-centered object perception.

Abstract Despite the fact that we necessarily view objects from one particular position, we generally achieve representations of them that transcend that special viewpoint. Shape constancy can be regarded as illustrating such object-centered perception. Nonetheless, there are cases where we fail to achieve such representations and an experiment with this outcome is described here. Three-dimensional wire objects were employed that were viewed nearby with all cues to depth available. Displacement of such a three-dimensional object brings about a considerable qualitative change in the shape of its retinal image. After viewing the objects in a particular position, recognition was subsequently tested when the object either (a) remained in the same position, (b) was displaced laterally from upper left to lower right or vice versa, or upper right to lower left or vice versa, or (c) changed its position as in b but was rotated to produce the same retinal projection as in a. The result was an appreciable drop in the recognition of the objects in b, the displacement of which resulted in an altered retinal projection. Some reasons were suggested for this dominance of the viewer-centered (or egocentric) character of perception resulting in failure in the achievement of object-centered representation.

Illusory Contours as the Solution to a Problem

The perception of certain figures with illusory contours entails a reversal of figure and ground. It is hypothesized that this process occurs in two stages. First, some factor must suggest or cue the reversal. Experiments are described that isolate three such factors, namely, alignment of physically present contours, recognized incompletion of parts of the stimulus array, and set. Once cued, however, other experiments indicate that in a further stage of processing the solution is examined with respect to its compatibility with the stimulus display or with other perceptual properties to which the display gives rise. Only if such compatibility is present will the perception of a figure with illusory contours be maintained.

The effect of knowledge of reversibility on the reversibility of ambiguous figures

The role of knowledge of the reversibility of reversible figures was tested in four experiments. Two ambiguous figures, the vase-face figure and a depth-reversing pyramid-hallway figure were shown to high school students. In the Uninformed condition, subjects were not told that the figures were reversible. A sampling procedure was used in which subjects reported what they perceived at 5-sec intervals. Viewing durations of up to 3 min were used, and approximately half of all subjects did not reverse at all during the uninformed condition, whereas virtually all subjects reversed quickly and frequently once they knew that the figures were reversible. These results are not consistent with neural fatigue models of perceptual reversal.

Stroboscopic Movement Based on Perceptual Intelligence

Stroboscopic movement perception can be viewed as the solution on the part of the perceptual system of the problem posed by the alternating appearance and disappearance of the stimulus objects. Under typical conditions there is no information provided which could account for such inexplicable stimulus change, so that movement is the most ‘plausible’ solution. If, however, such information is provided, other solutions may be preferred, and motion will not be perceived. In several experiments it is demonstrated that, when an object alternately covers and uncovers two dots, movement is not perceived, provided (a) the object is in the location in front of where a dot had just appeared rather than to the side of this location, and (b) the object appears to be solid or opaque rather than outline. Under such conditions the dots appear to be permanently present entities undergoing covering and uncovering. This effect does not require that a physical object with edges progressively occlude and disocclude the dots, since a moving phenomenal square based on subjective contours only and a stroboscopically moving square also eliminate or minimize perceived movement of the dots. Control experiments employing the same spatial and temporal intervals show that, without the information supporting the covering—uncovering solution, movement typically is perceived. These findings are interpreted as supporting the theory that perception results from a process analogous to intelligent problem solving.

The perception and recognition of complex figures

Abstract Although simple, novel figures seen only once establish relatively enduring memories, certain nuances of more complex figures do not seem to establish adequate traces at all. Experiments demonstrated that those features of a figure which are immaterial to its over-all, global shape are typically not recognized even immediately afterward; whereas those same features exposed in isolation under the same conditions and for the same period of time are recognized. It was concluded that, by and large, these features are not perceived, at least in the sense of being cognitively apprehended. Therefore, they fail to establish memories.

Speed constancy as a function of size constancy

If perceived velocity were to be a function of phenomenal extent traversed per unit time, speed constancy would be derivable from size constancy. Experiments were performed to test this possibility in which visible frames of reference were eliminated. With cues to distance, judgments ofspeed approached constancy; without such cues, judgments of speed were in terms of rate ofimage displacement.

Intelligence Factors in the Perception of Form through a Moving Slit

When a narrow slit moves over a line figure (or the equivalent stimulus is simulated by a short line segment appropriately displacing within a moving slit), observers often perceive an extended figure although the stimulus information is ambiguous. In several experiments it is shown that the perception of a figure tends to occur, provided the stimulus information is compatible with the perceptual ‘solution’ of a figure revealed by a moving aperture: the visible segment of the figure must completely fill the aperture, the surround of the aperture must appear to be opaque and extend an adequate distance on both sides, the aperture must be perceived as an opening rather than as a figure, and, if the slope of the segment is visible, it must change appropriately from moment to moment. Thus the outcome can be thought of as an intelligent, elegant solution to the problem posed by the transforming proximal stimulus.

The Optomotor Response and Induced Motion of the Self

Although the optomotor response in animals and induced motion of the self in humans occur under very similar stimulus conditions, they have not hitherto been related. Experiments with fish are reported which support the hypothesis that the optomotor response is based on the animals attempt to nullify the unwanted experience of its own motion that is imposed upon it.

Induced movement based on subtraction of motion from the inducing object.

Induced movement occurs not only when an object surrounding a stationary one moves below threshold but when it moves above threshold. The above-threshold effect is particularly puzzling and seemingly irrational because the relative displacement should be fully accounted for by perceiving the moving object in motion. The accepted theory has been that such excess motion can be explained in terms of a separation of systems: The enclosed object is governed by the relationship to its immediately surrounding frame of reference, and the latter is governed either by the relationship to its surrounding frame of reference or to the observer. An alternative explanation is that when induced motion occurs, the moving object is perceived to be either stationary or moving less than is warranted by its actual motion. Evidence is presented supporting this hypothesis according to which the relative displacement is apportioned phenomenally to either the induced object, the inducing object, or both. The objective motion of the inducing object is thus in whole or part transferred to the induced object. Thus, excess phenomenal motion does not occur, and induced movement can be regarded as the rational solution to a problem.