Rethinking perceptual organization: The role of uniform connectedness

A principle of perceptual organization, calleduniform connectedness (UC), is described, and a theoretical approach to perceptual organization is proposed in which this principle plays a fundamental role. The principle of UC states that closed regions of homogeneous properties—such as lightness, chromatic color, texture, and so forth—tend to be perceived initially as single units. We demonstrate its effects and show that they occur even when opposed by powerful grouping principles such as proximity and similarity. We argue that UC cannot be reduced to such grouping principles, because it is not a form of grouping at all. We then propose a theoretical framework within which UC accounts for the initial (orentry level) organization of the visual field into primitive units. Classical principles of grouping operate after UC, creating superordinate units consisting of two or more basic-level units. Parsing processes also operate after UC, dividing basic-level units into subordinate parts. UC in the retinal image is proposed to be a necessary, but not a sufficient, condition for unit formation, since connected elements on the retina that are perceived to lie in separate depth planes fail to be perceived as units. This fact, together with other evidence that the Gestalt principles of grouping are based onperceived (rather than retinal) relations, suggests that the organization of visual stimulation into UC objects is ultimately achieved within a relatively late, postconstancy representation of environmental surfaces. The implications of this possibility are discussed in light of present theories of visual perception.     

On the nature and order of organizational processing: A reply to Peterson

Several points in the original article by Palmer and Rock (1994) are clarified in light of Peterson’s (1994) commentary. First, we address several issues related to the nature and order of organizational processes in our theory. We argue that many of her objections result from misconceptions about our theory. We attempt to clarify the relevant issues, including the fact that we intended the theory to describe an ordering of processes in cascade rather than as a sequence of classical discrete stages. Second, we discuss Peterson’s objections to our discussion of her findings on the relation between figure-ground processing and object recognition. We argue against her “prefigural recognition” proposal on logical grounds and provide an alternative account of her findings in terms of our theory.     

Perception without attention: results of a new method.

Having found by the use of a new method for examining perception without attention that grouping and texture segregation do not seem to occur (see Mack, Tang, Tuma, Kahn, & Rock (1992) Cognitive Psychology, 24, we go on to ask what is perceived without attention using this new method. Our subjects receive only one inattention trial in a sequence of trials involving a visual distraction task. In addition to the distraction task in the inattention trial, subjects received a stimulus of which they had no prior knowledge or expectation and were questioned or tested directly afterward for their perception of that stimulus. Two subsequent trials containing test stimuli serve as within-subject controls. The results of a series of experiments indicate that the presence of one or more stimulus objects and their locations are preattentively perceived, as is their color, but shape is not. Because individual items are detected without attention, we conclude that perceptual organization is initially based on a principle in which connected regions of uniform stimulation are inferred to be discrete units (the principle of uniform connectedness). One striking, unexpected finding is that without attention many subjects have no awareness at all of the stimulus object, an effect we call inattentional blindness.     

Immediate correction and adaptation based on viewing a prismatically displaced scene

It was shown that when observers view a scene of a room through displacing prisms there is an immediate correction of the prismatic distortion. Objects appear to lie in a direction closer to their true direction than to that produced by the refraction of the prisms. It was also shown that a brief period of exposure to the prismatically viewed scene, without movement or sight of the body, results in substantial adaptation to the displacement.     

Inattentional blindness as a function of proximity to the focus of attention.

The effect of the distance between the center of the focus of attention and an unexpected stimulus on detection was examined in two experiments with the use of the inattentional-blindness paradigm [Mack and Rock, 1998 Inattentional Blindness (Cambridge, MA: MIT Press)]. In experiment 1, the closer a stimulus was to the center of attention, the more likely it was to be detected. Experiment 2 replicated this finding and controlled for retinal eccentricity. These results suggest that low-level stimulus characteristics (e.g. location) may play an important role in the detection of unexpected stimuli. The data are consistent with previous research on the spatial aspects of attention demonstrating that the distance to the focus of attention is a critical variable. This study demonstrates that the effect of distance is similar under conditions of inattention. Theories put forward to explain inattentional blindness should include 'early' attentional factors, as well as factors resulting from later stages of processing.     

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 preceptual properties to which the display gives rise. Only if such compatibility is present will the perception of a figure with illusory contours be maintained.