Chapter 11 Multiple sources of information influence time-to-contact judgments: Do heuristics accommodate limits in sensory and cognitive processes?

Abstract There is an increasing number of studies which indicates that judgments about time-to-contact (TTC) are influenced by multiple sources of information and are constrained by threshold factors and cognitive operations. In this chapter, I provide an overview of these studies and attempt to provide a framework for studying TTC judgments based on five hypotheses: (a) TTC judgments are based on multiple sources of information, including heuristics (e.g., pictorial depth cues) and invariants (e.g., tau); (b) The sources of information that influence TTC judgments are determined, in part, by limits in sensory processes and (c) by limits in cognitive processes; (d) The sources of information that influence TTC judgments vary throughout a task or event;(e) Apparent spatial extent and mental structure can influence TTC judgments. Support for these hypotheses is presented. It is concluded that the effectiveness of tau is constrained by limits in sensory and cognitive processes and that it is adaptive for the visual system to rely on other sources of information including heuristics, which serve to accommodate such limits and to provide flexibility in performance. Such limits also play an, important role in determining which sources of information are effective throughout a task or event. Future research should consider the role of limitations in sensory and cognitive processes in models of TTC perception determine the effective sources of information for TTC judgments throughout a task or event, and measure the relative strengths and combinatorial rules of these sources. There is an increasing number of studies which indicates that judgments about TTC and related tasks are influenced by multiple sources of information and are constrained by threshold factors and cognitive operations. In this chapter, I provide an overview of these studies, focusing on research that my collaborators and I have conducted since 1989. In doing so, I hope to provide a framework for studying judgments of time to contact. This framework is based on five hypotheses around which this chapter is organized. These hypotheses are introduced below, but first a note on terminology is in order. In this chapter, I discuss judgments about collision and non-collision events. These include judgments of time to contact (or time to collision, time to arrival, arrival time, time to passage) and judgments about, whether a collision would occur (or potential collision, collision detection) rather than when a collision would occur. Here “ TTC ” refers generally to the time to completion of any such event rather than specifically to time to contact. The phrase “TTC judgments” includes these related tasks. Also, the generic term optical TTC information refers to visual information that veridically specifies any TTC event, such as local τ or global τ. Unless noted, the studies described in this chapter involved computer simulations of such events. In the five main sections of this chapter, I present an overview of research that supports each of the following hypotheses. In the final section, I conclude that heuristics play an important role in TTC judgments and consider reasons that they would do so. I begin with a list of the hypotheses and a brief introduction to how each is supported. This serves as a preview of what will be detailed in the main sections of the chapter. Hypothesi 1. TTC judgments are based on multiple sources of information, including heuristics and invariants. Heuristics are implicated by findings that TTC judgments are influenced by pictorial depth information, including relative size (the size-arrival effect ), height in field, and occlusion. This makes it necessary to determine how effects combine when multiple sources of information are available. Other relevant data include measures of TTC judgments when optical TTC information or one of its components is nullified (by manipulating optic flow via self motion, or occluders). Hypothesis 2. The sources of information that influence TTC judgments are determined, in part, by limits in sensory processes. Limits in sensory processes are implicated by findings that (a) TTC judgments are influenced by lower-order motion which does not specify TTC unequivocally, such as optical magnification, expansion rate, and image velocity; (b) TTC judgments are not affected by irregularities in optical TTC information due to computer aliasing. This suggests that TTC information is not extracted on a frame-by-frame basis, possibly due to limits in the temporal resolution of the visual system; (c) TTC judgments are affected by retinal eccentricity, and attention instructions, which suggests that useful information for such judgments may not be accessible to the observer within a single glance or attentional act. Hypothesis 3. The sources of information that influence TTC judgments are determined, in part, by limits in cognitive processes. Limits, in cognitive processes are implicated by findings that TTC judgments are affected by the number of objects in the display (set size) in a manner consistent with limited-capacity processing and limits in memory. Other studies of TTC judgments implicate cognitive motion extrapolation and visual imagery. Hypothesis 4. The sources of information that influence TTC judgments vary throughout a task or event. Studies indicate that it is difficult to identify a critical value of a single source of information that accounts for TTC judgments. For example analyses of a collision-avoidance task and relative TTC judgments indicated that optical size, change in optical size, rate of expansion, or TTC, did not consistently account for performance. However, such analyses assume that the information sources that govern performance remain constant throughout a task. This seems unlikely because the quality of some sources of depth information varies with distance. Alternatively, information sources that influence TTC judgments vary as the distances between the observer and objects in the environment change. This is adaptive and provides flexibility in performance. Hypothesis 5. Apparent spatial extent and mental structure can influence TTC judgments. Apparent spatial extent is implicated by findings that TTC judgments are affected by visual illusions such as the Sander parallelogram illusion. Mental structure is implicated by effects of perceptual set or intention on TTC judgments, particularly a coupling between apparent TTC and apparent depth.