Visual masking: past accomplishments, present status, future developments.
Bottom Line: However, visual masking also has been a phenomenon deemed worthy of study in its own right.Most of the recent uses of visual masking have focused on the study of central processes, particularly those involved in feature, object and scene representations, in attentional control mechanisms, and in phenomenal awareness.Key issues and problems are discussed with the aim of guiding future empirical and theoretical research.
Affiliation: Department of Psychology, University of Houston.
Visual masking, throughout its history, has been used as an investigative tool in exploring the temporal dynamics of visual perception, beginning with retinal processes and ending in cortical processes concerned with the conscious registration of stimuli. However, visual masking also has been a phenomenon deemed worthy of study in its own right. Most of the recent uses of visual masking have focused on the study of central processes, particularly those involved in feature, object and scene representations, in attentional control mechanisms, and in phenomenal awareness. In recent years our understanding of the phenomenon and cortical mechanisms of visual masking also has benefited from several brain imaging techniques and from a number of sophisticated and neurophysiologically plausible neural network models. Key issues and problems are discussed with the aim of guiding future empirical and theoretical research.
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Mentions: A series of experiments conducted by Corthout et al. (Corthout, Uttl, Walsh, Hallett, & Cowey, 1999; Corthout, Uttl, Ziemann, Cowey, & Hallett, 1999) demonstrated masking effects of transcranial magnetic stimulation (TMS) on foveal targets consisting of individual letters. Figure 4 shows typical results (Corthout, Uttl, Ziemann et al., 1999) of TMS masking as a function of the SOA between the TMS pulse and the visual target. Negative and positive SOAs indicate that the TMS onset respectively preceded and followed the onset of the visual target. Masking magnitude is indicated by the proportion of correct identifications of the target letters, with lower proportions corresponding to stronger masking. Note that two masking maxima were obtained, one at an SOA of –30 ms and the other at an SOA of 100 ms. Corthout, Uttl, Ziemann et al. (1999) concluded – rightly in my opinion – that these two maxima corresponded to the TMS-induced disruption of two processing intervals, the former corresponding to the early feedforward activation of cortical neurons and the latter to activation depending on re-entrant feedback from higher cortical visual areas. This interpretation dovetails nicely with the aforementioned proposal of Lamme and co-workers (Lamme, 2001; Lamme & Spekreijse, 2000; Lamme et al., 2000; Super et al., 2001) regarding an early feedforward and stimulus-dependent component and a later re-entrant and percept-dependent component of V1 neural responses.
No MeSH data available.