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

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

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

5. A Schematic of What vs. Where

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

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

9. Artwork pre and post achromatopsia

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

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

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

13. A Schematic of What vs. Where ACRHOMOTOPSIA AKINETOPSIA

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