Graded vs. Quantal Allocation of Attention and Awareness

Abstract

The Attentional Blink (AB) refers to the profound impairment in consciously detecting the second of two targets presented serially among distractors, when that second target (T2) occurs within 500ms of the first (T1). The AB paradigm has recently been used to investigate whether conscious perception is a graded or quantal (all-or-none) state, with conflicting results (Sergent & Dehaene, 2004; Nieuwenhuis & de Kleijn, 2011). This discrepancy may stem from the use of indirect methods that probed the participants’ subjective reports of conscious states rather than probing the quality of the conscious content per se. To address this issue, here we used a mixture modeling approach (Zhang & Luck, 2008) that independently estimates the probability of consciously perceiving a target and the precision at which that target is perceived. By measuring representational quality across temporal intervals in the AB we can directly infer whether limitations of temporal attention lead to graded (as expressed by changes in perceived target precision) or all-or-none (as expressed by changes in probability of target perception) changes in conscious percepts. We found that the probability of consciously perceiving T2 was strongly affected by the SOA between T1 and T2 but the precision at which that target was perceived remained unaffected. This was the case for both simple (colors) and complex (faces) stimuli, and across AB paradigms (RSVP and skeletal ABs). In a final experiment we varied the amount of attention available for T2 processing by manipulating the extent to which T1 captured attention. With increased attention to T1, there was a reciprocal decrease in the probability of consciously perceiving T2, but no effect on its precision. These results suggest that conscious perception is all-or-none in the AB, and that attention acts as a capacity-limited resource that modulates the probability of occurrence of this quantal percept.

Meeting abstract presented at VSS 2012