Academic journal article Psychonomic Bulletin & Review

Seeing Faces in the Noise: Stochastic Activity in Perceptual Regions of the Brain May Influence the Perception of Ambiguous Stimuli

Academic journal article Psychonomic Bulletin & Review

Seeing Faces in the Noise: Stochastic Activity in Perceptual Regions of the Brain May Influence the Perception of Ambiguous Stimuli

Article excerpt

Research on binocular rivalry and motion direction discrimination suggests that stochastic activity early in visual processing influences the perception of ambiguous stimuli. Here, we extend this to higher level tasks of word and face processing. In Experiment 1, we used blocked gender and word discrimination tasks, and in Experiment 2, we used a face versus word discrimination task. Stimuli were embedded in noise, and some trials contained only noise. In Experiment 1, we found a larger response in the N170, an ERP component associated with faces, to the noise-alone stimulus when observers were performing the gender discrimination task. The noise-alone trials in Experiment 2 were binned according to the observer's behavioral response, and there was a greater response in the N170 when they reported seeing a face. After considering various top-down and priming-related explanations, we raise the possibility that seeing a face in noise may result from greater stochastic activity in neural face-processing regions.

A basic goal of cognitive neuroscience is to link behavior with neural mechanisms. Two notable successes have come from research on binocular rivalry and motion direction discrimination, in which an ambiguous stimulus is presented and physiological correlates are found between the reported percept and ongoing activity in visual areas such as Vl and MT (Britten, Newsome, Shadlen, Celebrini, & Movshon, 1996; Britten, Shadlen, Newsome, & Movshon, 1993), as well as in extrastriate areas (Tong, Nakayama, Vaughan, & Kanwisher, 1998). In the present work, we seek to generalize this principle to the domains of word and face processing, which also may involve specialized neural areas in the inferotemporal cortex (Kanwisher, Stanley, & Harris, 1999; but see also Gauthier, Tarr, Anderson, Skudlarski, & Gore, 1999, for evidence of expertise effects in the same area). Whereas prior work has been done with single-cell and fMRI recording, here we rely on known response properties of electrophysiological (EEG) measures.

In the present study, we address the relation between face-related brain activity and the reported percept by embedding faces and words in noise and using noisealone displays to create an ambiguous stimulus. We will rely on the N170 component of the event-related potential (ERP)1, which has been linked to activity in face-related regions of the human. Jeffreys (1989) has shown that Mooney faces elicit a negative-going component that occurs 170 msec after stimulus onset. However, when these faces are inverted, they are difficult to interpret as a face, and the N170 is likewise attenuated. Numerous subsequent studies have also shown that faces elicit a strong N170 component (Bentin, 1997; Bentin, Allison, Puce, Perez, & McCarthy, 1996; Olivares & Iglesias, 2000). This downward deflection is largest over the temporal lobes (Bentin et al., 1996). Although there is some disagreement as to the precise neural locus of the N170, its latency and spatial location suggest that it represents activity in regions typically associated with early perceptual processing of faces and other complex visual stimuli.

In addition to these bottom-up factors, perceptual expertise and context modulate the N170. Tanaka and Curran (2001) found a larger N170 component in bird and dog experts for faces of animals on which an individual was an expert. Rossion, Gauthier, Goffaux, Tarr, and Crommelinck (2002) trained observers to individuate novel objects called greebles, and found expertise effects in the N170. To demonstrate contextual effects, Bentin and colleagues (Bentin & Golland, 2002; Bentin, Sagiv, Mecklinger, Frederici, & von Cramon, 2002) presented pairs of dots that evoked only a weak N170 response to observers. The dots were subsequently shown surrounded by face features that made them interprétable as eyes. After priming with a face context, the N170 response to the dots alone increased. …

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