C BBB - CHAPTER 7: THE SEEING BRAIN

Sensation

The effects of a stimulus on the sensory organs.

Perception

The elaboration and interpretation of a sensory stimulus based on, for example, knowledge of how objects are structured.

Simple cells

Cells that respond to different orientations but also respond to points of light.

Complex cells

Cells that combine the responses of several simple cells, have larger receptive fields and require stimulation along their entire length.

Hyper complex cells

Cells that combine the responses of several complex cells, but unlike complex cells they are sensitive to length as well as orientation.

Achromatopsia

The effect where people see the world in black and white because of damage to their V4 area.

V4

A region of the extrastriate cortex associated with color perception.

V5/MT

A region of the extrastriate cortex associated with motion perception.

Prosopagnosia

Impairments of face processing that do not reflect difficulties in early visual analysis.

Imagery

Perception in reverse.

Retina

The internal surface of the eye consisting of multiple layers, including photoreceptors and neurons.

Rod cells

A type of photoreceptor specialized for low levels of light intensity.

Cone cells

A type of photoreceptor specialized for high levels of light intensity and different wavelengths.

Receptive field

The region of space that elicits a response from a given neuron.

Blind spot

The point at which the optic nerve leaves the eye and where no rods or cones are present.

Primary visual cortex (or V1)

The first stage of visual processing in the cortex that combines simple visual features into more complex ones.

Simple cells in vision

Cells that respond to light in a particular orientation or points of light along that line.

Complex cells in vision

Cells that respond to light in a particular orientation but not to single points of light.

Hyper complex cells in vision

Cells that respond to particular orientations and particular lengths.

Hemianopia

Cortical blindness restricted to one half of the visual field.

Quadrantanopia

Cortical blindness restricted to a quarter of the visual field.

Scotoma

A small region of cortical blindness.

Retinotopic organization

The organization of receptive fields reflecting the spatial organization present in the retina.

Blindsight

A symptom in which a patient reports not consciously seeing stimuli but can nevertheless perform visual discriminations accurately.

Ventral stream (in vision)

A pathway extending from the occipital lobes to the temporal lobes involved in object recognition, memory and semantics.

Dorsal stream (in vision)

A pathway extending from the occipital lobes to the parietal lobes involved in visually guided action and attention.

Akinetopsia

A failure to perceive visual motion.

Color constancy

The color of a surface is perceived as constant even when illuminated in different lighting conditions.

Biological motion

The ability to detect whether a stimulus is animate or not from movement cues alone.

Structural descriptions

A memory representation of the three-dimensional structure of objects.

Apperceptive agnosia

A failure to understand the meaning of objects due to a deficit at the level of object perception.

Associative agnosia

A failure to understand the meaning of objects due to a deficit at the level of semantic memory.

Figure–ground segregation

The process of segmenting a visual display into objects versus background surfaces.

Lateral occipital complex (LOC)

A region of the brain specialized for processing object shapes.

Integrative agnosia

A failure to integrate parts into wholes in visual perception.

Object constancy

An understanding that objects remain the same irrespective of differences in viewing condition.

Adaptation (or repetition suppression)

A reduced neural response to a repeated stimulus or stimulus feature.

Category specificity

The notion that the brain represents different categories in different ways or regions.

Face recognition units (FRUs)

Stored knowledge of the three-dimensional structure of familiar faces.

Person identity nodes (PINs)

An abstract description of people that links perceptual knowledge with semantic knowledge.

Fusiform face area (FFA)

An area in the inferior temporal lobes that responds more to faces than other visual objects.

Categorical perception

The tendency to perceive ambiguous or hybrid stimuli as one thing or the other.

Photoreceptors

Specialized cells in the retina that convert light into neural signals.

Fovea

The central region of the retina containing the highest density of cone cells and providing the sharpest vision.

Visual illusion

A discrepancy between physical reality and visual perception that reveals how the visual system processes information.

Holistic processing

The tendency to process an object, especially a face, as a whole rather than as separate parts.

Mental rotation

The ability to mentally manipulate and rotate representations of objects.

Inferotemporal cortex

A region of the ventral visual stream involved in object recognition and categorical processing.

Motion perception

The ability to perceive movement within the visual environment.

Categorical face perception

The tendency to perceive ambiguous facial stimuli as belonging to one category rather than another.

The earliest stage in visual processing

Involves basic elements such as edges and bars of various lengths, contrasts and orientations.

The second stage in visual processing

Involves grouping elements into higher-order units that code depth cues and segregate surfaces into figure and ground.

The third stage in visual processing

The viewer-centred description is matched onto stored three-dimensional descriptions of object structure.

The fourth stage in visual processing

Meaning is attributed to the stimulus and other information becomes available.

The gestalt principle 1 - The law of proximity

Visual elements are more likely to be grouped if they are closer together.

The gestalt principle 2 - The law of similarity

Elements are grouped together if they share visual attributes.

The gestalt principle 3 - The law of good continuation

Edges are grouped together to avoid changes or interruptions.

The gestalt principle 4 - The law of closure

Missing parts are filled in.

The gestalt principle 5 - The law of common fate

Elements that move together tend to be grouped together.

Retinal ganglion cells

Neurons in the retina whose axons form the optic nerve and carry visual information to the brain.

Center-surround receptive field

A receptive field in which the center and surrounding area respond oppositely to light.

Lateral geniculate nucleus (LGN)

A thalamic processing station between the retina and primary visual cortex.

Geniculostriate pathway

The visual pathway from the retina to the LGN and then to primary visual cortex.