Processing the Trees and the Forest During Initial Stages of Face Perception: Electrophysiological Evidence
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Processing the Trees and the Forest during Initial Stages of Face Perception: Electrophysiological Evidence Shlomo Bentin1, Yulia Golland1, Anastasia Flevaris2,3, Lynn C. Robertson2,3, and Morris Moscovitch4,5 Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/18/8/1406/1756323/jocn.2006.18.8.1406.pdf by guest on 18 May 2021 Abstract & Although configural processing is considered a hallmark of elicited by line-drawn schematic faces compared to line-drawn normal face perception in humans, there is ample evidence that schematic objects, no N170 effect was found if a pair of small processing face components also contributes to face recognition objects substituted for the eyes in schematic faces. However, if and identification. Indeed, most contemporary models posit a a pair of two miniaturized faces substituted for the eyes, the dual-code view in which face identification relies on the analysis N170 effect was restored. Additional experiments ruled out an of individual face components as well as the spatial relations explanation on the basis of miniaturized faces attracting atten- between them. We explored the interplay between processing tion independent of their location in a face-like configuration face configurations and inner face components by recording and show that global and local face characteristics compete for the N170, an event-related potential component that manifests processing resources when in conflict. The results are discussed early detection of faces. In contrast to a robust N170 effect as they relate to normal and abnormal face processing. & INTRODUCTION or local face-related information takes precedence Configural processing is considered a hallmark of nor- when they lead to different initial interpretations of mal face perception in humans (e.g., McKone, Martini, the visual input. & Nakayama, 2001; Tanaka & Sengco, 1997; Hosie, The N170 effect is defined as the considerably larger Ellis, & Haig, 1988; Rhodes, 1988; Haig, 1984; see a amplitude of the first visual negative potential (mea- review in Farah, Wilson, Drain, & Tanaka, 1998). How- sured at posterior lateral sites) elicited after the onset of ever, there is ample evidence that face components are a human face compared to other stimulus categories, processed independently during face recognition and such as human hands, other animal-faces, watches, play an important role in face identification (e.g., birds, items of furniture, tools, houses, and so forth Cabeza & Kato, 2000; Macho & Leder, 1998). Indeed, (e.g., Itier & Taylor, 2004; Carmel & Bentin, 2002; most contemporary views posit a dual-code according Bentin et al., 1996). This effect is more robust (although to which face recognition relies on the extraction of slightly delayed) in response to face components (par- featural codes, that is, local analysis of individual face ticularly to eyes) and to inverted faces than to full, components, as well as on the extraction of configural upright faces. Bentin and Golland (2002) and Sagiv codes, that is, the computation of the spatial relations and Bentin (2001) suggested that it is associated with among the face components (e.g., Cabeza & Kato, an early visual mechanism for detecting face-relevant 2000; Searcy & Bartlett, 1996). In the present study, information. According to this interpretation, the N170 we analyzed the N170 face-sensitive event-related po- effect should appear whenever the visual stimulus is tential (ERP) component (Bentin, Allison, Puce, Perez, sufficiently suggestive of a face, whether by its individ- & McCarthy, 1996) to explore how global processing of ual (local) shape or by its global spatial configuration. the face configuration and local processing of the eyes Supporting this hypothesis is the fact that the N170 interact during face categorization and whether global effect is elicited not only by isolated recognizable face components but also by schematically drawn faces whose individual components are simple marks in the 1Hebrew University of Jerusalem, Jerusalem, Israel, 2University locations of the eyes, nose, and mouth. In the latter of California at Berkeley, 3Veterans Administration Medical Cen- case, their face-related value is revealed only by their ter, Martinez, 4University of Toronto, Canada, 5Rotman Research spatial configuration (Sagiv & Bentin, 2001). Further- Institute, Toronto, Canada more, previous studies showed that scrambling the D 2006 Massachusetts Institute of Technology Journal of Cognitive Neuroscience 18:8, pp. 1406–1421 Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/jocn.2006.18.8.1406 by guest on 03 October 2021 global configuration of natural face components does EXPERIMENT 1 not reduce the N170 effect (Zion-Golombic & Bentin, In the present experiment, the most interesting stimuli 2006; Bentin et al., 1996). However, it is unknown to address the questions outlined in the introduction whether the inverse relationship is also true. Are per- were schematic faces in which small-size objects substi- ceptual decisions based on the global configuration tuted for regular eyes in schematic faces (Figure 1, top influenced by the shape of its local components? To row). In addition to the faces with object-eyes, line-drawn address this question, we contrasted local and config- objects and regular schematic faces (i.e., faces with mean- ural processing in face perception when each of these ingless shapes or tokens as eyes) were presented in processes leads to a different initial interpretation of Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/18/8/1406/1756323/jocn.2006.18.8.1406.pdf by guest on 18 May 2021 separate blocks of trials to serve as baseline ERPs for the stimulus. nonface and face stimuli, respectively (Figure 1, middle In a seminal study using nonface stimuli, Navon and bottom rows). Participants pressed a button in re- (1977) studied local and global processing by building sponse to predesignated targets (schematic drawings of ‘‘global’’ letters using sets of repeated ‘‘local’’ letters flowers) that occurred only occasionally. If configural- as building blocks. Faster identification of global than based processing preempts local processing of the ob- local letters suggested a global processing precedence. jects within the face, we should observe an N170 effect— Using similar procedures with neurological patients, that is, the visual system should respond to such stimuli Robertson and Lamb (1991) described a more com- just as it responds to normal schematic faces. However, plex perceptual mechanism in which the right and left if local processing of the component objects prevails, the hemispheres are biased to process global or local in- object-perception mechanism should be activated and formation, respectively, coordinating their actions and no N170 effect should be observed. providing different levels of hierarchically organized spa- tial structures; a separate mechanism combines this in- formation to form a coherent percept (see also Hubner Methods & Volberg, 2004). Whereas initial awareness of global aspects of a stimulus could be the default of the percep- Participants tual system (cf. Hochstein & Ahissar, 2002), task, per- The participants were 12 undergraduates from Hebrew ceiver, and stimulus factors can influence the relative University with normal or corrected-to-normal vision. emphasis placed on local or global aspects to influence They were paid or participated for course credits and gave the overt response (Lamb & Robertson, 1988). For in- signed, informed consent as approved by the internal stance, even when only the global pattern of a stimulus review board at Hebrew University before testing began. is relevant, local information could affect global pro- cessing, with global information being brought to aware- Stimuli ness later, if at all. In Experiment 1, we directly contrast local- and configural-based interpretations of a stimulus The stimuli were drawn using computer software. Three in face-like stimuli. types of face stimuli were used (Figure 1): 75 schematic Figure 1. Design of Experiment 1 and examples of stimuli used in all experiments. Bentin et al. 1407 Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/jocn.2006.18.8.1406 by guest on 03 October 2021 faces (faces with meaningless shapes as eyes), 75 line- outer canthus of the right eye and the other at the drawn objects, and 75 faces with object-eyes (configu- supraorbital region of the same eye. Both the EEG and rations of faces in which two identical objects were EOG were referenced to an electrode placed at the tip reduced in size, substituting for the eyes in the schemat- of the nose. Throughout the EEG recording, the elec- ic faces). In addition, 45 drawn flowers were included trodes’ impedance was kept under 5 k . as targets in an oddball paradigm (see below). Each Event-related potentials resulted from averaging EEG stimulus was presented only once in the course of the epochs of 1000 msec starting 100 msec prior to stimulus experiment. onset. Average waveforms were computed for each subject separately for each stimulus condition and were Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/18/8/1406/1756323/jocn.2006.18.8.1406.pdf by guest on 18 May 2021 digitally filtered with a band-pass of 0.8 to 17 Hz (3 dB/ Task and Design octave). Trials contaminated by EOG and/or EEG arti- An oddball monitoring procedure was used in which facts were excluded from the average by an automatic participants were instructed to silently count the num- rejection algorithm with a threshold amplitude of ber of targets presented in a block of trials and to ignore ±100 mV. No ERP was based on less than 50 trials. the other stimuli. Targets were flowers of different The amplitude and the latency of N170 were the kinds, and the different faces and objects were non- dependent variables for statistical analysis. This ERP targets (distracters) presented in separate blocks of component was defined as the most negative peak trials. A block contained 9 to 13 targets and 75 dis- between 120 and 210 msec from stimulus onset. Based tracters, presented in random order.