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Jeroen J.A. van Boxtel, Christof Koch; Afterimage duration and its modulation by attention and consciousness. Journal of Vision 2009;9(8):121. doi: https://doi.org/10.1167/9.8.121.
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In recent years the study of the link between attention and conscious perception has intensified. Some reports claim that attention and conscious perception are intrinsically linked, while others claim that they are two independent processes. Strong evidence for the second proposal could be gained from a finding that paying attention to a stimulus and the conscious perception of that stimulus have opposing influences on the stimulus' processing. Here we report such evidence. We measured the influence of attention and conscious perception (i.e. visibility) on processing of a visual stimulus, by measuring the afterimage duration of that stimulus. The visual stimuli were gratings, presented monocularly, and peripherally during a 4-sec adaptation phase. A uniform average-luminance field followed this phase, and observers used button presses to indicate how long an afterimage was visible. During the adaptation phase attention and visibility were independently modulated. Attention was modulated by having the observers perform (or not perform) an attention-absorbing Rapid Serial Visual Presentation (RSVP) letter counting task at fixation during the adaptation. Visibility was modulated by presenting (or not presenting) a strong variant of binocular rivalry, continuous flash suppression (Tsuchiya & Koch 2005), in the eye contra-lateral to the adaptor. We found that increased attention to the stimulus reduced afterimage duration (Wilcoxon signed-rank test p [[lt]]0.01; see also Suzuki & Grabowecky 2003; Lou 2001), while increased visibility (i.e. the absence of CFS) of the stimulus increased afterimage duration (Wilcoxon signed-rank test p[[lt]]0.026). These findings show that attention and conscious perception are dissociable processes with potentially opposing effect on the stimulus' processing.
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