Biomedical subjects

P C Gerhardstein

Publications and source records attributed to P C Gerhardstein.

3 recordsLinked to original sources

PubMed2000

Object memory effects on figure assignment: conscious object recognition is not necessary or sufficient.

In three experiments we investigated whether conscious object recognition is necessary or sufficient for effects of object memories on figure assignment. In experiment 1, we examined a brain-damaged participant, AD, whose conscious object recognition is severely impaired. AD's responses about figure assignment do reveal effects from memories of object structure, indicating that conscious object recognition is not necessary for these effects, and identifying the figure-ground test employed here as a new implicit test of access to memories of object structure. In experiments 2 and 3, we tested a second brain-damaged participant, WG, for whom conscious object recognition was relatively spared. Nevertheless, effects from memories of object structure on figure assignment were not evident in WG's responses about figure assignment in experiment 2, indicating that conscious object recognition is not sufficient for effects of object memories on figure assignment. WG's performance sheds light on AD's performance, and has implications for the theoretical understanding of object memory effects on figure assignment.

Aged↗

PubMed1997

High level object recognition without an anterior inferior temporal lobe.

Seven individuals with unilateral anterior inferior temporal (AIT) lobectomies performed two types of shape recognition tasks with line drawing of 3D objects briefly presented in either the left or the right visual field. In one task, subjects named familiar objects in a name priming paradigm. In the other task, subjects judged whether two objects, presented sequentially with an intervening mask, were the same or different in shape, disregarding differences in orientation of up to 60 degrees in depth. They could not use names or basic level concepts to do the matching as the stimuli were either nonsense objects or, if familiar objects, were of same name-different-shaped exemplars on different trials. The disadvantage of presenting an image to the lobectomized hemisphere was negligible in both tasks. Two non-exclusive possibilities are suggested by this result: (a) Object recognition is completed posterior to AIT, likely at the temporal-occipital boundary, with no deleterious retrograde effects on object recognition from the AIT section, or (b) Callosal transfer of object information prior to AIT is completely efficient. These results, along with results of single unit recording and lesion experiments in the monkey, PET and MRI imaging in humans, and a plausibility argument based on the pattern of callosal connections suggest both are correct. Rather than mediating real-time object recognition, AIT may code representations for visual episodes and scenes.

Adult↗

PubMed1993

Recognizing depth-rotated objects: evidence and conditions for three-dimensional viewpoint invariance.

Five experiments on the effects of changes of depth orientation on (a) priming the naming of briefly flashed familiar objects, (b) matching individual sample volumes (geons), and (c) classifying unfamiliar objects (that could readily be decomposed into an arrangement of distinctive geons) all revealed immediate (i.e., not requiring practice) depth invariance. The results can be understood in terms of 3 conditions derived from a model of object recognition (I. Biederman, 1987; J. E. Hummel & I. Biederman, 1992) that have to be satisfied for immediate depth invariance: (a) that the stimuli be capable of activating viewpoint-invariant (e.g., geon) structural descriptions (GSDs), (b) that the GSDs be distinctive (different) for each stimulus, and (c) that the same GSD be activated in original and tested views. The stimuli used in several recent experiments documenting extraordinary viewpoint dependence violated these conditions.

Adolescent↗