Chapter 3: Visual Perception Flashcards
Lens
The transparent tissue located near the front of each eye that (together with the cornea) plays an important role in focusing incoming light. Muscles control the degree of curvature of the lens, allowing the eye to form a sharp image on the retina.
Cornea
The transparent tissue located near the front of each eye that plays an important role in focusing incoming light.
Retina
The light-sensitive tissue that lines the back of the eyeball.
Photoreceptors
Cells on the retina that are sensitive to light and that respond (i.e. send a signal to adjacent cells) when they are stimulated by light (rods and cones are the two types of photoreceptor).
Rods
Photoreceptors that are sensitive to very low light levels but that are unable to discriminate hues and that have relatively poor activity. Often contrasted with cones.
Cones
Photoreceptors are able to discriminate hues and that have high acuity. Cones are concentrated in the retina’s fovea and become less frequent in the visual periphery. Often contrasted with rods.
Acuity
The ability to see fine detail.
Fovea
The center of the retina and the region on the eye in which acuity is best; when a person looks at an object, they are lining up that object with the fovea.
Bipolar Cells
A type of neuron in the eye. Bipolar cells receive their input from the photo and transmit their output to the retinal ganglion cells.
Ganglion Cells
A type of neuron in the eye. The ganglion cells receive their input from the bipolar cells, and then the axons of the ganglion cells gather together to form the optic nerve, carrying information back to the lateral geniculate nucleus.
Optic Nerve
The bundle of nerve fibers, formed from the retina’s ganglion cells, that carries information from the eyeball to the brain.
Lateral Geniculate Nucleus (LGN)
An important way station in the thalamus that is the first destination for visual information sent from the eyeball to the brain.
Lateral Inhibition
A pattern in which cells, when stimulated, inhibit the activity of neighboring cells. In the visual system, lateral inhibition in the optic nerve creates edge enhancement.
Edge Enhancement
A process created by lateral inhibition in which the neurons in the visual system give exaggerated responses to edges of surfaces.
Single-Cell Recording
A technique for recording the moment-by-moment activation level of an individual neuron within a healthy, normally functioning brain.
Receptive Field
The portion of the visual field to which a cell within the visual system responds. If the appropriately shaped stimulus appears in the appropriate position, the cell’s firing rate will change. The firing rate will not change if the stimulus is of the wrong form or is in the wrong position.
Center-Surround Cells
A type of neuron in the visual system that has a “donut-shaped” receptive field. Stimulation in the center of the receptive field has one effect on the cell; stimulation in the surrounding ring has the opposite effect.
Area VI
The site on the occipital lobe where axons from the LGN first reach the cerebral cortex. This site is (for one neural pathway) the location at which information about the visual world first reaches the brain.
Parallel Processing
A system in which many steps are going on at the same time (e.g.: rods and cones). Usually contrasted with serial processing.
What System
The system of visual circuits and pathways leading from the visual cortex to the temporal lobe and especially involved in object recognition. Often contrasted with the where system.
Where System
The system of visual circuits and pathways leading from the visual cortex to the parietal lobe and especially involved in the spatial localization of objects and in coordination of movements. Often contrasted with the what system.
Binding Problem
The problem of reuniting the various elements of a scene, given that these elements are initially dealt with by different systems in the brain.
Neural Synchrony
A pattern of firing by neurons in which neurons in one brain area fire at the same time as neurons in another area; the brain seems to use this pattern as an indication that the neurons in different areas are firing in response to the same stimulus.
Conjunction Errors
An error in perception in which a person correctly perceives what features are present but misperceives how the features are joined, so that – for example – a red circle and a green square might be misperceived as a red square and a green circle.
