Figure 2.7. Number of neural impulses in selected single cells of the monkey brain when shown differing pictures. These neurons fire the most when a face is present (Washmuth et al. 1994).

Figure 2.8. (a) Rembrandt van Rijn, Anatomy Lesson of Dr. Tulp, Oil on canvas, 162 cm x 217 cm. Mauritshuis, The Hague. (b) Eye tracking diagram from Molnar (1981).

Stimulus image Figure 2.9. (a) Image with 4 bands of differing brightness. A to D are locations marks. (b) Physical brightness levels of image in (a). (c) Perceptual brightness of image (a) "seen" by viewer resulting from lateral inhibition. (d) Conceptual diagram of how lateral inhibition can enhance borders between parts of the visual field of different brightness (Goldstein, 2002). Here A to F refer to cells. Cells A, B, and C faithfully convey greater brightness (100 units) than cells D, E, and F (20 units) to the neurons directly behind them in the next layer. All cells send neural inhibition in proportion to the brightness levels (10%) to cells situated next door in the next neural layer (i.e., laterally). The output at the next layer of neurons (bottom in figure) has a slightly brighter "hairline" on the brighter side of the image(88 vs 80 units); and a slightly darker "hairline" on the darker side (8 vs 16 units). The units of brightness were selected as an example.

Retinas Retinas with 3 layers of neurons Right Visual Field – light goes to left side of retinas Left visual Field – light goes to right side of retinas Light Optic nerves – axons of ganglion cells that are located in retinas The Thalamus, a subcortical structure. Visual information passes through the lateral geniculate nucleus of the thalamus. Occipital lobes of Cortex, 1 st place in cortex receiving information about visual scene; called V1 (Vision 1). Figure Drawing of the visual system.

Visual Pathway – Simplified LIGHT reflected from the image EYE – mechanical parts (e.g., lens, fluid in eye-ball) RETINA of EYE (neural parts - lining at back) Layer 1: RECEPTORS Layer 2: BIPOLAR CELLS Layer 3: GANGLION CELLS (axons form optic nerve to brain) BRAIN 1 st Nucleus in THALAMUS (mid-brain structure) lateral geniculate nucleus 2 nd CORTEX a. Striate cortex at back of brain –V1 b. 2 Streams Ventral: Inferior-temporal (IT – around sides of brain) Dorsal: Medial-temporal (MT – up over middle of brain) Change light to neural impulses Integrate light info – (e.g., enhance edges) Integrate vision with other senses Receive info in higher brain What is seen Where is object Passing light representing image faithfully Figure Verbal description of steps in the visual pathway.

Two Visual Streams in Cortex What stream - Object identity Shapes of Objects and Colors recognized here Ventral route (around sides of brain) Pathway: V1 to V2 to V3 to V4 to Inferior Temporal (IT) lobe Animals without IT cannot do task to discriminate between two objects(food under a circular shape; not under a square). Humans with damage in what path cannot name objects they see. Where/How stream – Motion and Action Spatial arrangement, motion, depth recognized here Dorsal route (over top of brain) Pathway: V1 to V2 to V3 to V5 = Medial Temporal (MT) lobe Animals without MT cannot do task based on locatio (left bin has the food). Humans with damage in the Where/How path cannot do spatial tasks such as setting a table. Figure Two streams of neural information about vision in cortex that are postulated by neuroscientists.