1 / 14

Last Lecture

Vision. Last Lecture. Organization of the Visual System continued Blindsight What/Where pathways Their discovery, their neural retinal origins. This Lecture. What/Where pathways their manifestations in humans Examining the what pathway The Visual Agnosias.

bernad
Download Presentation

Last Lecture

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Vision Last Lecture • Organization of the Visual System continued • Blindsight • What/Where pathways • Their discovery, their neural retinal origins

  2. This Lecture • What/Where pathways • their manifestations in humans • Examining the what pathway • The Visual Agnosias

  3. Single Units & Receptive Fields • Location(s) on sensory surface that causes cell firing (spatial r.f.). • Region of the retina from which a cell gets input. • Stimulus attributes that cause cell firing. • Motion • wavelength (color) • shape • Specialized modules monitoring the world for the attributes that “turn them on” • consist of cells with specific receptive field properties

  4. A Schematic of What vs. Where

  5. What vs. Where in Humans • Focal lesions produce selective color or motion blindness. • cortical color blindness (achromatopsia) • motion blindness (akinetopsia) • Positron Emission Tomography (PET) studies in Humans reveal: • Motion Area distinct from color area • (e.g. Zeki and colleagues, 1990.)

  6. Achromatopsia • Inability to perceive color-- color knowledge and color naming can be intact. • acquired after cortical brain damage • distinct from congenital color blindness (photoreceptor abnormality) • Subjective reports... • Lesion locus: bilateral occipito-temporal lesions associated w/upper visual field deficits.

  7. Artwork pre and post achromatopsia

  8. Akinetopsia: Motion blindness due to focal brain damage (Zihl and colleagues, 1983) Characteristics of this famous case: • no blindness as assessed by perimetry • mild calculation and speech difficulties • all other aspects of vision are within normal range • subjective reports... • Lesion locus: input to dorsal pathway (V5/MT)

  9. PET Activation Study Logic • Perceptual/cognitive activity mediated by localized neural activity. • Blood flow changes accompany regional changes in neural activity. • Blood flow changes measured by monitoring distribution of radioactive tracer.

  10. Regions active in response to COLOR Regions active in response to MOTION

  11. A Schematic of What vs. Where AKINETOPSIA ACRHOMOTOPSIA

  12. Attribute-specific deficits • Reveal unique functions performed by distinct areas. • Special purpose modules perform operations in parallel. • Functions of many modules still undefined. • Consider deficits of form, object recognition...

More Related