Two visual systems and two theories of perception: An attempt to reconcile the constructivist and ecological approaches

Abstract

The two contrasting theoretical approaches to visual perception, the constructivist and the ecological, are briefly presented and illustrated through their analyses of space and size perception. Earlier calls for their reconciliation and unification are reviewed. Neurophysiological, neuropsychological, and psychophysical evidence for the existence of two quite distinct visual systems, the ventral and the dorsal, is presented. These two perceptual systems differ in their functions; the ventral system's central function is that of identification, while the dorsal system is mainly engaged in the visual control of motor behavior. The strong parallels between the ecological approach and the functioning of the dorsal system, and between the constructivist approach and the functioning of the ventral system are noted. It is also shown that the experimental paradigms used by the proponents of these two approaches match the functions of the respective visual systems. A dual-process approach to visual perception emerges from this analysis, with the ecological-dorsal process transpiring mainly without conscious awareness, while the constructivist-ventral process is normally conscious. Some implications of this dual-process approach to visual-perceptual phenomena are presented, with emphasis on space perception.

Visual information underpinning skilled anticipation: The effect of blur on a coupled and uncoupled in situ anticipatory response

“…As was predicted by Hypothesis 1.3, the coupled response condition demonstrated a degree of resilience to blur, with 3.00D required to reduce RA to the 50% level achievable by guessing (Figure 2). This finding suggests that visual clarity is not critical for coupled anticipation and is consistent with the expectation that a low level of blur would not adversely affect functions produced via the dorsal visual stream (which relies on a relatively poor quality of visual acuity; Brown, Halpert, & Goodale, 2005;Livingstone & Hubel, 1988;Norman, 2002). In contrast to the response for coupled anticipation, even with clear (habitual) vision, uncoupled anticipation was not different from chance guessing levels; rather curiously, however (and in contrast to Hypothesis 1.4), performance tended frequency visual information.…”

“…Although these particular tasks would not be considered to be visually onerous, this resilience to blur has been replicated in an interceptive striking task (cricket batting) which is much more likely to require fine online visual-motor manipulations (Mann, Abernethy, & Farrow, 2010b;Mann, Ho, De Souza, Watson, & Taylor, 2007). Collectively, these results are consistent with Norman's (2002) conceptualization of visual clarity being a limitation to ventrally based but not dorsally based tasks. As a result, it appears reasonable to propose that if visual clarity is a limitation to perceptual performance, low levels of blur may be expected to adversely affect a ventrally based task but not a dorsally based one.…”

“…Given the proposition that coupled and uncoupled responses are sourced by different types of visual information, we expected to find that visual blur would have a different effect, depending on the degree of perception-action coupling used in the anticipatory response (an interaction effect; Hypothesis 1.2). Consistent with the predictions of Norman (2002) that visual clarity would not limit the performance of a dorsally based task, it was hypothesized that the coupled response would demonstrate some degree of resilience to blur (Hypothesis 1.3). In contrast, it was expected that performance in the uncoupled condition would immediately and progressively decrease as the level of visual blur increased (Hypothesis 1.4).…”

“…In an examination of driving performance, Higgins, Wood, and Tait (1998) found that the introduction of blur resulted in an immediate decrease in contextually relevant perceptual judgments such as road sign recognition, road hazard avoidance, and total driving time; yet the blur had no effect on the ability of participants to drive through targets. Norman (2002) interpreted these findings to be a result of visual blur limiting the performance of ventrally dependent perceptual tasks but not that of dorsally dependent motor tasks. Jackson, Abernethy, and Wernhart (2009) recently investigated the effect of visual blur on the anticipation of skilled tennis players.…”

An allocentric rather than perceptual deficit in patient D.F.

“…Although some of the evidence for the model has been criticized (e.g. the evidence from visual illusions [4][5][6] , and the evidence from optic ataxia 7 ), the perception/action dissociation found in DF is still widely accepted as convincing evidence for the model 8 . Here I have examined the possibility that what has been described as a perception/action dissociation in DF may in reality be a dissociation between different modes of visuospatial processing, namely object-based spatial metrics (allocentric mode) versus observer-based metrics (egocentric mode).…”