UBC Theses and Dissertations
A cognitive effect of a moving object’s dynamic visual history : spatiotemporal integration of physical properties Gibbs, Brian J.
Despite enormous informational complexity in the optical environment, the visual world is effortlessly seen as coherent. Indeed, an object may change in virtually all of its physical properties and in its spatial location and yet maintain a constant perceptual identity. Apparently pieces of information registered in different segments of space-time, but referring to the same object, are perceptually integrated. Kahneman, Treisman and Gibbs (in progress) explored the cognitive organization corresponding to this perceptual organization; the present thesis represents an extension of their work. To study the spatiotemporal integration of information regarding moving objects they developed the preview paradigm. The prototypical visual display of this paradigm consists of three phases: (a) Letters are presented, each within a line-figure object, and are then removed (field-1), (b) the empty objects move to new positions, (c) letters are again presented in the objects and a marker appears, cueing one of them (field-2). The task is to name the letter in the cued object. The critical reaction time (RT) comparison is between consistent conditions (the target letter is previewed in the target object) and inconsistent conditions (the target letter is previewed, but in another object). An RT advantage for consistent conditions is termed the object effect because it represents object-specific facilitation. Object effects were generated in many experiments, including one utilizing only apparent motion to create objects. Certain experiments suggested that the object effect does not occur at a lexical or semantic level, but involves information concerning physical properties. The present thesis further explores the physical nature of the information integration underlying the object effect. Preview experiments were conducted, typically not with a letter-naming task, but with tasks requiring stimulus identification on the basis of a particular physical property. In experiments utilizing four moving line figures, object effects were obtained with presence and size. These effects were not artifacts of attending to field-1 or of confusing field-1 with field-2. In experiments utilizing apparent motion, object effects were obtained with color and with letters. Duodimension experiments elaborated the paradigm by introducing variation on a response-irrelevant dimension. The presence object effect was reduced by response-irrelevant shape inconsistency; the size object effect was eliminated by response-irrelevant shape inconsistency; the color object effect was unaffected by response-irrelevant letter-shape inconsistency; the letter object effect was slightly reduced by response-irrelevant color inconsistency. The duodimension results suggest that the object-specific representation underlying the object effect consists of somewhat conjoined properties. This has implications for the role of attention in the object effect, and inspires the speculation that motion might be special with respect to attention. Accounts of the object effect rival to Kahneman et al.'s can be proposed: that it results from the integration of response tendencies rather than stimulus information, that it is based on a decrease in apparent distance between stimuli rather than on their unitization, and that its seeming retroactivity is an illusion produced by the relative quickness with which low spatial frequencies are processed. The present results support arguments against each of these accounts. The general conclusion of this thesis is that the spatiotemporal integration underlying the object effect does involve information about physical properties.
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