Neural Signatures of Conscious Face Perception in an Inattentional Blindness Paradigm

Abstract

Previous studies suggest that early stages of face-specific processing are performed preattentively and unconsciously, whereas conscious perception emerges with late-stage (Ͼ300 ms) neuronal activity. A conflicting view, however, posits that attention is necessary for face-specific processing and that early-to-mid latency neural responses (ϳ100 -300 ms) correspond more closely with perceptual awareness. The current study capitalized on a recently developed method for manipulating attention and conscious perception during EEG recording (modified inattentional blindness paradigm) and used face stimuli that elicit a well known marker of early face processing, the N170 event-related potential (ERP). In Phase 1 of the experiment, subjects performed a demanding distracter task while line drawings of faces and matched control stimuli were presented in the center of their view. When queried, half of the subjects reported no awareness of the faces and were deemed inattentionally blind. In Phase 2, subjects performed the same distracter task, but now consciously perceived the face stimuli due to the intervening questioning. In Phase 3, subjects performed a discrimination task on the faces. Two primary contrasts were made: aware versus unaware (equally task irrelevant) and task-relevant versus task-irrelevant (equally aware). The N170 and a subsequent ERP component, the visual awareness negativity (ϳ260 -300 ms), were absent during inattentional blindness and present in the aware conditions. The P3b (Ͼ300 ms) was absent for task-irrelevant faces, even when consciously perceived, and present only when the faces were task relevant. These results inform contemporary theories of conscious face perception in particular and visual attention and perceptual awareness in general.

The experiential blink: Mapping the cost of working memory encoding onto conscious perception in the attentional blink

“…One inconsistent set of findings in the literature are a number of impressive studies that ascribe a post-perceptual locus for the P3 (Pitts, Padwal, Fennelly, Martínez, & Hillyard, 2014;Shafto & Pitts, 2015;Squires, Hillyard, & Lindsay, 1973). Our experiment though has a number of differences to these previous studies, which presumably explain the difference in findings.…”

“…Indeed, it could be that there is an earlier process in the timecourse, which we do not see in our EEG experiments. Possibilities for such a component are the modulation of the P2 (Vogel, et al, 1998) or the N2 (Sergent, et al, 2005), which might be related to the Visual Awareness Negativity (Shafto & Pitts, 2015). This said, we present empirical evidence that the P3 was modulated by subjective visibility in our experimental setting -this is our key finding.…”

“…2) The elegant demonstration by Pitts and colleagues (Pitts, et al, 2014;Shafto & Pitts, 2015) that the P3 in their experiment was modulated by task set, does not naturally carry over to our setting. This is because task set, certainly in respect of instruction, is constant throughout our experiment.…”

Dissociation between the neural correlates of conscious face perception and visual attention

“…For the P1 and N170, we selected time windows using the same procedure in Navajas et al (); we considered 40‐ms windows centered in the peak of each component (110–150 ms for the P1, 170–210 ms for the N170). For the P3, we used a 200‐ms window centered in its peak (300–500 ms), as in previous studies (Pitts et al, ; Shafto & Pitts, ).…”

“…In fact, with the peak amplitude of this signal, it was possible to decode above chance the subjects' conscious reports. One limitation of this study, which also applies to most related studies (Aru et al, ; Fisch et al, ; Pitts, Martínez, & Hillyard, ; Pitts, Metzler, & Hillyard, ; Sergent, Baillet, & Dehaene, ; Shafto & Pitts, ), is that the observed modulations in the neural responses might just reflect trial‐by‐trial fluctuations of attention rather than the perceptual state of the observer (Navajas, Rey, & Quian Quiroga, ). In other words, the difference between the seen and unseen conditions may be due to a varying allocation of attentional resources.…”