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The two sides of face perception: Asymmetric cerebral activation associated with featural and configural processing
NemoImage
11, Number
5, 2000, Part 2 of 2 Parts ID
Ial@
PERCEPTION
The Two Sides of Face Perception: Asymmetric Cerebral Activation Associated with Featural and Configural Processing Ken A. Pa&r*, Michael W. Parsor@, Marcia Grabowecky*, Andrew R. Mayer?, Stephen M. Raot *Department of Psychology, Northwestern University, Evanston, IL, USA TDepartment of Neurology, Medical College of Wisconsin, Milwaukee, WI, USA Both cerebral hemispheres ordinarily receive visual input when a face is viewed, yet they do not process this input in the same way. It has long been supposed that a face is treated as a perceptual unit in the RH, whereas salient features that can be labeled are emphasized in the LH. Recent conceptualizations appeal to an initial filtering and segregation of spatial frequency information (relatively lower frequencies to RI-I, higher to LH). Visual deficits following unilateral damage to the temporoparietal junction and functional neuroimaging of normal subjects using nonface stimuli support this global/local characterization of functional aaymmetries. Fmthermm e, patterns of d&its in agnosia suggest that critical RH contributions to face recognition may be based on configural processing; LH contributions may reflect featnral processing. We investigated these hypotheses using an attentional manipulation designed to preferentially engage configural or featural face processing. Attention was directed to just the nose, the whole face, or away from the face (Nose, Face, and Symbol tasks, respectively). Stimulus factors were held constant across these three conditions. We hypothesized that configurahfeatural functional asymmetries would appear in face-selective areas of the fusiform gyms (FFA) and in other brain regions. Methods Whole-brain fh4RI (1 ST GE-Signa) was conducted on 18 right-handed individuals, Fach trial included a central face and lateral geometric symbols presented simultaneously. Faces were created through subtle alterations to a single face. The tasks were variations on a “l-back task” in which subjects responded according to whether there was a match between current and prior stimuli based on different stimulus dimensions (nose, configuration of facial features, or symbols, in Nose, Face, and Symbol tasks, respectively). There was also a rest condition and a control condition in which the Symbol task was performed with a scrambled face. Order of task blocks was counterbalanced and each block included a task cue and 10 trials (6OOms stimulus, 15OOm.s fixation). Stimulus changes were randomized and occurred in each stimulus dimension independently, with stimuli counterbalanced across task. Following 12 repetitions of each task, subjects performed Nose* and Face* tasks wherein stimulus changes occurred only on the relevant dimension. Task-related activity was calculated using multiple regression. Resulting measures of signal intensity change were analyzed using repeated-measures ANOVA (statistical threshold p<.OOO5, cluster threshold 250 microliter). Region-of-interest (ROI) analyses were also conducted.
Performance was more accurate in the Nose task (84%) than in the Face task (74%). Likewise, accuracy was higher in the Nose* task (88%) than in the Face* task (81%). Accuracy was high in the Symbol task with faces (92%) and scrambled faces (93%). Imaging results from the Symbol task with faces versus scrambled faces revealed a strong fusiform activation. However, the primary comparisons (Face vs. Nose; Face* vs Nose*) did not reveal fusiform activation in either voxel-wise or ROI analyses. Functional asymmetries were apparent in other brain regions (see Figure). In common to Face/Nose and Face*/Nose* contrasts, attending to the nose resulted in activation within the left inferior (BA 40) and superior (BA 5/7) parietal areas. Attending to facial configuration resulted in activation of the right middle/inferior (BA 46) and medial (BA 8) frontal regions. Discussion Although functional asymmetries were observed, results may not generalize to situations in which face discriminations are not so subtle. In addition, the greater perceived difficulty of the Face task relative to the other tasks may have influenced the pattern of results. Nonetheless, several tentative conclusions can be made. The absence of FFA asymmetries suggests that face processing in this region does not vary as a function of directing attention to different parts of the face, which is understandable if FPA activity reflects early processes of face detection. Configural/featnral attentional biases may occur at a later processing stage. Results from a companion study using the identical task design while event-related potentials were recorded may be useful for characterizing the time-course of face processing (e.g., lateralized Face/Nose differences at posterior temporal scalp began about 250 ms after face onset). Gur findings that other regions showed functional asymmetries in the form of LH activations for featural processing and RH activations for configural processing may coincide with previous neuroimaging results from contrasts between global and local processing of hierarchical letter stimuli, although there are important differences. Given that the most robust asymmetries were in parietal cortex for attention to nose and in frontal cortex for attention to whole face, confignral and featural biases in face processing may be implemented in quite different ways.
Supported
by NIH
grants
MH51358
and MH57836
to S.M.R.
and NS34639
S712
to K.A.P.
11, Number
5, 2000, Part 2 of 2 Parts ID
Ial@
PERCEPTION
The Two Sides of Face Perception: Asymmetric Cerebral Activation Associated with Featural and Configural Processing Ken A. Pa&r*, Michael W. Parsor@, Marcia Grabowecky*, Andrew R. Mayer?, Stephen M. Raot *Department of Psychology, Northwestern University, Evanston, IL, USA TDepartment of Neurology, Medical College of Wisconsin, Milwaukee, WI, USA Both cerebral hemispheres ordinarily receive visual input when a face is viewed, yet they do not process this input in the same way. It has long been supposed that a face is treated as a perceptual unit in the RH, whereas salient features that can be labeled are emphasized in the LH. Recent conceptualizations appeal to an initial filtering and segregation of spatial frequency information (relatively lower frequencies to RI-I, higher to LH). Visual deficits following unilateral damage to the temporoparietal junction and functional neuroimaging of normal subjects using nonface stimuli support this global/local characterization of functional aaymmetries. Fmthermm e, patterns of d&its in agnosia suggest that critical RH contributions to face recognition may be based on configural processing; LH contributions may reflect featnral processing. We investigated these hypotheses using an attentional manipulation designed to preferentially engage configural or featural face processing. Attention was directed to just the nose, the whole face, or away from the face (Nose, Face, and Symbol tasks, respectively). Stimulus factors were held constant across these three conditions. We hypothesized that configurahfeatural functional asymmetries would appear in face-selective areas of the fusiform gyms (FFA) and in other brain regions. Methods Whole-brain fh4RI (1 ST GE-Signa) was conducted on 18 right-handed individuals, Fach trial included a central face and lateral geometric symbols presented simultaneously. Faces were created through subtle alterations to a single face. The tasks were variations on a “l-back task” in which subjects responded according to whether there was a match between current and prior stimuli based on different stimulus dimensions (nose, configuration of facial features, or symbols, in Nose, Face, and Symbol tasks, respectively). There was also a rest condition and a control condition in which the Symbol task was performed with a scrambled face. Order of task blocks was counterbalanced and each block included a task cue and 10 trials (6OOms stimulus, 15OOm.s fixation). Stimulus changes were randomized and occurred in each stimulus dimension independently, with stimuli counterbalanced across task. Following 12 repetitions of each task, subjects performed Nose* and Face* tasks wherein stimulus changes occurred only on the relevant dimension. Task-related activity was calculated using multiple regression. Resulting measures of signal intensity change were analyzed using repeated-measures ANOVA (statistical threshold p<.OOO5, cluster threshold 250 microliter). Region-of-interest (ROI) analyses were also conducted.
Performance was more accurate in the Nose task (84%) than in the Face task (74%). Likewise, accuracy was higher in the Nose* task (88%) than in the Face* task (81%). Accuracy was high in the Symbol task with faces (92%) and scrambled faces (93%). Imaging results from the Symbol task with faces versus scrambled faces revealed a strong fusiform activation. However, the primary comparisons (Face vs. Nose; Face* vs Nose*) did not reveal fusiform activation in either voxel-wise or ROI analyses. Functional asymmetries were apparent in other brain regions (see Figure). In common to Face/Nose and Face*/Nose* contrasts, attending to the nose resulted in activation within the left inferior (BA 40) and superior (BA 5/7) parietal areas. Attending to facial configuration resulted in activation of the right middle/inferior (BA 46) and medial (BA 8) frontal regions. Discussion Although functional asymmetries were observed, results may not generalize to situations in which face discriminations are not so subtle. In addition, the greater perceived difficulty of the Face task relative to the other tasks may have influenced the pattern of results. Nonetheless, several tentative conclusions can be made. The absence of FFA asymmetries suggests that face processing in this region does not vary as a function of directing attention to different parts of the face, which is understandable if FPA activity reflects early processes of face detection. Configural/featnral attentional biases may occur at a later processing stage. Results from a companion study using the identical task design while event-related potentials were recorded may be useful for characterizing the time-course of face processing (e.g., lateralized Face/Nose differences at posterior temporal scalp began about 250 ms after face onset). Gur findings that other regions showed functional asymmetries in the form of LH activations for featural processing and RH activations for configural processing may coincide with previous neuroimaging results from contrasts between global and local processing of hierarchical letter stimuli, although there are important differences. Given that the most robust asymmetries were in parietal cortex for attention to nose and in frontal cortex for attention to whole face, confignral and featural biases in face processing may be implemented in quite different ways.
Supported
by NIH
grants
MH51358
and MH57836
to S.M.R.
and NS34639
S712
to K.A.P.