Abstract
The role of stereo disparity in the recognition of 3-dimensional (3D) object shape remains an unresolved issue for theoretical models of the human visual system. We examined this issue using high-density (128 channel) recordings of event-related potentials (ERPs). A recognition memory task was used in which observers were trained to recognize a subset of complex, multipart, 3D novel objects under conditions of either (bi-) monocular or stereo viewing. In a subsequent test phase they discriminated previously trained targets from untrained distractor objects that shared either local parts, 3D spatial configuration, or neither dimension, across both previously seen and novel viewpoints. The behavioral data showed a stereo advantage for target recognition at untrained viewpoints. ERPs showed early differential amplitude modulations to shape similarity defined by local part structure and global 3D spatial configuration. This occurred initially during an N1 component around 145–190 ms poststimulus onset, and then subsequently during an N2/P3 component around 260–385 ms poststimulus onset. For mono viewing, amplitude modulation during the N1 was greatest between targets and distracters with different local parts for trained views only. For stereo viewing, amplitude modulation during the N2/P3 was greatest between targets and distracters with different global 3D spatial configurations and generalized across trained and untrained views. The results show that image classification is modulated by stereo information about the local part, and global 3D spatial configuration of object shape. The findings challenge current theoretical models that do not attribute functional significance to stereo input during the computation of 3D object shape.
Highlights
The role of stereo disparity in the recognition of 3-dimensional (3D) object shape remains an unresolved issue for theoretical models of the human visual system
For stereo viewing there was a higher frequency of significant differences between targets and shared parts (SD) nontargets in the left hemisphere only, 2(1) ϭ 4, p ϭ
We observed differential amplitude modulations of evoked potentials to targets and nontargets defined by shared parts (SD; locally similar) or shared spatial configuration (DS; globally similar) starting at the N1 component between 145 and 200 ms poststimulus onset
Summary
The role of stereo disparity in the recognition of 3-dimensional (3D) object shape remains an unresolved issue for theoretical models of the human visual system. The contribution of stereo input is not ruled out, but neither explicitly incorporated into the proposed theoretical framework (e.g., Biederman, 1987; Leek, Reppa, & Arguin, 2005; Ullman, 2007) This contrasts with theoretical models that have attributed functional significance to certain kinds of stereo-defined shape information in object recognition—such as the computation of local surface depth orientation, and the specification of 3D object structural descriptions (Marr & Nishihara, 1978). It is more likely to be used to supplement shape information derived from mono-ocular cues when object recognition (i.e., target/nontarget discrimination or view generalization) is facilitated by the derivation of 3D object structure In support of this hypothesis, they showed that stereo input facilitates the classification of complex multipart 3D objects across large, but not small, changes in depth rotation. The results showed later modulation of ERP amplitude during an N2 component between 240 and 370 ms for stereo and mono input that was linked to the perceptual matching of shape.
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