study guide 2

Trichromatic theory (component theory)

There are 3 kinds of color receptor cells (cones). Each cone has is sensitive to a wavelength. Color is based on relative firing of cone type.

Three theories of perception

Trichromatic theory, opponent-process theory, retinex theory

Opponent-process theory

proposed by Ewald Hering in 1878.

two different classes of cells in the visual system for encoding color and another for encoding brightness. the complementary colors hyperpolarize while its opposite color is depolarized.

Retinex theory

perceived color of one part of a scene is influenced by the surrounding context. only theory that takes in to consideration of top down/bottom up processing.

what are the two halves of the retina

temporal hemiretina (near temples), nasal hemiretina (near the nose)

what pathway crosses over in the visual pathway (decussate)

Nasal hemiretina

what is the spot called where the visual pathways cross

Optic Chiasm

route from eyes to brain

retina, lateral geniculate nucleus (LGN) of the thalamus, primary visual cortex (V1)/ striate cortex.

Retinotopic

adjacent points on the retina correspond to adjacent points on other parts of the visual system ie. LGN and primary visual cortex.

how many layers does the lateral geniculate nucleus have

6 layers, 3 layers for each eye

parvocellular

top 4 layers of the LGN. contains small cell bodies responsive to color, fine details, and stationary/slow moving objects

Magnocellular

bottom two layers of the LGN. contain larger cell bodies responsive to movement.

Primary visual cortex V1 (striate cortex)

located in the occipital lobe, has 6 layers with pyramidal cells and interneurons.

what does the visual cortex process

tiny portions of the visual field. Cannot perceive whole objects or scenes here, multiple regions combine the visual information to form whole pictures

Secondary visual cortex (V2)

surrounds V1. receives information from V1 and does higher processing of visual stimuli (pre-striate cortex)

visual association cortex

other senses converge here

Ventral stream

what an object is. in the inferior temporal lobe, cells responsive to color, form, and shape of objects

Dorsal stream

where an object is. In the posterior parietal lobe. cells responsive to spatial information and movement of objects.

Simultanagnosia

A person can only attend to one stimulus at a time

Fusiform face area (FFA)

cluster of neurons in the inferotemporal lobe that respond selectively to faces

Para hippocampal place area

cluster of neurons near the hippocampus that fire selectively to natural scenes (landscapes)

Extrastriate body area

cluster of neurons in extrastriate cortex that selectively respond to body parts (not including faces)

Visual agnosia

disorder causing impairment or inability to recognize a visually presented object. damage to the ventral pathway.

Prosopagnosia

an inability to recognize faces. (can still perceive it is a face just not who it belongs to) caused by damage to the ventral pathway

Akinetopsia

inability to perceive smooth movement of objects. jumps from “picture” to “picture”. caused by damage to the V5 (MT/MST region) dorsal pathway

Scotoma

an area of blindness in the corresponding area of the contralateral visual field of both eyes

Hemianopsic

a scotoma covering half of the visual field

blindsight

the ability to respond to visual stimuli in a scotoma with no conscious awareness of them.

Rods

mediate achromatic, low acuity vision under dim light (scotopic vision)

Cones

mediate high acuity color vision in good lighting (photopic vision)

Transduction

conversion of one form of energy to another.

Visual transduction: conversion of light to neural signals by the visual receptors.

Rhodopsin

pigment in the eye that is “bleached” when exposed to light and regains light absorbing capacity when returned to darkness. helps facilitate rod-mediated vision.