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Related Experiment Videos

Object orientation agnosia: a failure to find the axis?

I M Harris1, J A Harris, D Caine

  • 1University of Sydney. irinah@npsych.rpa.cs.nsw.gov.au

Journal of Cognitive Neuroscience
|September 21, 2001
PubMed
Summary

Patients with Alzheimer's disease can exhibit a unique spatial deficit. This study details a case where object recognition was preserved, but orientation judgment was severely impaired, particularly for non-upright objects.

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Area of Science:

  • Neuroscience
  • Cognitive Psychology
  • Neurology

Background:

  • A dissociation between object recognition and orientation judgment is rare, typically seen in patients with vascular lesions.
  • Alzheimer's disease (AD) is a progressive neurodegenerative disorder primarily affecting memory and cognition.

Purpose of the Study:

  • To describe a case of probable Alzheimer's disease exhibiting a specific dissociation between object recognition and orientation judgment.
  • To investigate the neural underpinnings and cognitive mechanisms of this dissociation.

Main Methods:

  • Case study of a 57-year-old male with probable Alzheimer's disease.
  • Neuroimaging (hypometabolism in posterior cortical regions, especially postero-superior parietal lobes).
  • Experimental tasks assessing object recognition, orientation evaluation, and orientation discrimination.

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Main Results:

  • The patient demonstrated intact object recognition, independent of orientation, mediated by salient features.
  • Severe impairment in judging the orientation of non-upright objects, yet intact implicit knowledge of upright orientation.
  • Remarkably accurate orientation judgments for upside-down objects compared to other non-upright orientations.

Conclusions:

  • Object orientation judgments may rely on matching an object's principal axis to an internal representation.
  • Impaired orientation judgment in this AD patient suggests a failure in an "axis-finding" mechanism within the posterior parietal lobes.
  • This mechanism likely translates object-centered to eye-centered coordinates for visual guidance.