Academic journal article Attention, Perception and Psychophysics

Summation versus Suppression in Metacontrast Masking: On the Potential Pitfalls of Using Metacontrast Masking to Assess Perceptual-Motor Dissociation

Academic journal article Attention, Perception and Psychophysics

Summation versus Suppression in Metacontrast Masking: On the Potential Pitfalls of Using Metacontrast Masking to Assess Perceptual-Motor Dissociation

Article excerpt

Published online: 11 April 2014

# Psychonomic Society, Inc. 2014

Abstract A briefly flashed target stimulus can become "invisible" when immediately followed by a mask-aphenomenon known as backward masking, which constitutes a major tool in the cognitive sciences. One form of backward masking is termed metacontrast masking. It is generally assumed that in metacontrast masking, the mask suppresses activity on which the conscious perception of the target relies. This assumption biases conclusions when masking is used as a tool-for example, to study the independence between perceptual detection and motor reaction. This is because other models can account for reduced perceptual performance without requiring suppression mechanisms. In this study, we used signal detection theory to test the suppression model against an alternative view of metacontrast masking, referred to as the summation model. This model claims that target- and mask-related activations fuse and that the difficulty in detecting the target results from the difficulty to discriminate this fused response from the response produced by the mask alone. Our data support this alternative view. This study is not a thorough investigation of metacontrast masking. Instead, we wanted to point out that when a different model is used to account for the reduced perceptual performance in metacontrast masking, there is no need to postulate a dissociation between perceptual and motor responses to account for the data. Metacontrast masking, as implemented in the Fehrer-Raab situation, therefore is not a valid method to assess perceptual-motor dissociations.

Keywords Visual awareness . Perception and action . Signal detection theory . Confidence judgments . Reaction times

Visual backward masking has been a major tool in the exper- imental investigation of visual consciousness during the last decades (Ansorge, Francis, Herzog, & Ogmen, 2007;fora review, see Breitmeyer & Ogmen, 2000). It consists in pre- senting a mask shortly after a target stimulus. The latter is clearly visible when presented in isolation, but its presence may be difficult to report if it is closely followed by the mask.

One particular type of backward masking is called metacontrast masking. In metacontrast masking, the masked stimulus (typically a disk) and the masking stimulus (typically an annulus that covers the disk) share a contour but do not overlap. A standard interpretation of metacontrast masking posits that the mask-induced activations suppress the target- induced activations (Ansorge, Francis, et al., 2007).

On the basis of this idea, metacontrast masking has been used extensively as an experimental tool to vary the amount of target-related information that can be processed by the brain or to test whether the conscious perception of the target is a necessary prerequisite for other target-related processes (e.g., Lau & Passingham, 2006; Vorberg, Mattler, Heinecke, Schmidt, & Schwarzbach, 2003). One example is the Fehrer-Raab effect: Contrary to the target's visibility, simple reaction times (RTs) to a target ("respond as quicky as possible as soon as you detect") are unaffected by metacontrast masking. That is, the target continues to affect RTs, even under experimental conditions in which the mask turns the target (close to) "invisible" (e.g., Bernstein, Amundson, & Schurman, 1973; Fehrer & Biederman, 1962; Fehrer & Raab, 1962; Schiller & Smith, 1966; Taylor & McCloskey, 1990;for reviews, see Neumann & Klotz, 1994; Neumann & Scharlau, 2007). This result has been interpreted as strong evidence in favor of the independence of perceptual and motor responses (e.g., Neumann & Klotz, 1994; but see also Neumann & Scharlau, 2007; Waszak, Cardoso-Leite, & Gorea, 2007; Waszak & Gorea, 2004; for discussions about which criteria to rely on to make such interpretations, see Cardoso-Leite & Gorea, 2010; Reingold & Merikle, 1988; Schmidt & Vorberg, 2006). …

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