Lab write up due this Friday Proposal due

• Lab write up due this Friday • Proposal due Monday March 6 Late reports, one mark out of 20 for each day late.

Ch. 11 • Vision - central processes • Ultimately visual perception – Also: • Adjust size of the pupil • Direct eyes to the targets of interes • Regulate homeostatic behaviors to L/D cycle

Primary Visual Pathway

Primary Visual Cortex • AKA – Striate cortex – Brodmann’s area 17 or VI

Optic Disc

Blind Spot: Test your blind spot. Optic disc is located on the nasal side of the retina. With both eyes open, information about the corresponding region of visual space comes from the temporal side of the contralateral retina.

Blind Spot • With one eye, blind spot is undetected. • Why? – Visual cortex receptive fields fill in with cortical mechanisms that integrate information from the visual field (somehow).

Optic Disc

Optic Chiasm

Optic Tract

Decussation

Ganglion cell axons to lateral geniculate nucleus

Another target of ganglion cells: Pretectum co-ordinates pupillary light reflex

Another target of ganglion cells: suprachiasmatic nucleus (Retino-hypothalamic pathway)

Suprachiasmatic nucleus

Another target for ganglion cells: superior colliculus

RETINOTOPIC REPRESENTATION OF THE VISUAL FIELD • Each eye sees a part of the visual space that defines its visual field

Visual Field • Receive info from both fields • Nasal, temporal, superior and inferior divisions. • Binocular vision • Binocular hemifield

VISUAL FIELD • Temporal visual fields are more extensive than the nasal visual fields • Vision in the peripheral field is monoocular • Most of the rest of the visual field is seen by both eyes.

• Map is maintained in the LGN – Maintained by the visual cortex – Fovea is in the back of the visual cortex – Peripheral is progressively more anterior – Sensory surface reflects density of receptors

Upper visual field • Calcarine sulcus

Hubel and Weisel

Hubel and Weisel • Visual cortex responses using microelectrodes – Respond ot light/dark bars or edges – Only if in a particular orientation – Peak frequency depends on angle, preferred orientation – All edges representations were equally represented – Orientation selective neurons

Visual Cortex • Simple cells - Spatially distinct on and off zones • Complex cells - receptive field has a mixture of on and off zones • Length cells - respond to length of a bar that was moved across a receptive field • Direction cells - respond to direction of a bar moving across the receptive field.

• Still do not understand the mechanisms responsible for generating these selective responses.

Complex cell

Complex Cell

Binocular vision • Individual LGN neurons are mono-ocular driven. • How are neurons with different receptive fields arranged within the striate cortex? • A column of cells has similar response properties • Adjacent columns have similar response properties.

Visual Cortex • Composed of repeating units that contain all the neuronal machinery necessary to analyze a small region of visual space for a variety of different stimulus attributes.