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, 1632. 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, 1st place in cortex receiving information about visual scene; called V1 (Vision 1).

Figure 2.10. 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 1st Nucleus in THALAMUS (mid-brain structure)

lateral geniculate nucleus2nd CORTEX a. Striate cortex at back of brain –V1

b. 2 StreamsVentral: 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 2.11. 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 2.12. Two streams of neural information about vision in cortex that are postulated by neuroscientists.