The Seeing Brain
This chapter considers many examples of the constructive nature of the seeing brain (i.e., not just passively receiving information), from the perception of visual attributes, such as color and motion, up to the recognition of objects and faces. Light is converted into neural signals by the retina, and there are several routes by which this information is carried to the brain with the dominant routes (in humans and primates) being the geniculo-striate route to primary visual cortex (V1). V1 is a spatially-organized hub from which various other cortical routes emerge: a ventral route for object recognition (interfacing with memory and language) and a dorsal route (interfacing with attention and action). Disorders of object recognition are referred to as visual agnosia, and these have been traditionally subdivided into apperceptive agnosia and associative agnosia, depending on whether the deficit occurs at stages involved in perceptual processing or stages involving stored visual memory representations.
Multiple Choice Questions
Flashcards
The effects of a stimulus on the sensory organs
The elaboration and interpretation of a sensory stimulus based on, for example, knowledge of how objects are structured
The internal surface of the eyes that consists of multiple layers. Some layers contain photoreceptors that convert light to neural signals, and others consist of neurons themselves
A type of photoreceptor specialized for low levels of light intensity, such as those found at night
A type of photoreceptor specialized for high levels of light intensity, such as those found during the day, and specialized for the detection of different wavelengths
The point at which the optic nerve leaves the eye. There are no rods and cones present there
The first stage of visual processing in the cortex; the region retains the spatial relationships found on the retina and combines simple visual features into more complex ones
Primary visual cortex (or V1)
The region of space that elicits a response from a given neuron
In vision, cells that respond to light in a particular orientation (or points of light along that line)
In vision, cells that respond to light in a particular orientation but do not respond to single points of light
In vision, cells that respond to particular orientations and particular lengths
Cortical blindness restricted to one half of the visual field (associated with damage to the primary visual cortex in one hemisphere)
Cortical blindness restricted to a quarter of the visual field
A small region of cortical blindness
The receptive fields of a set of neurons are organized in a such a way as to reflect the spatial organization present in the retina
A symptom in which the patient reports not being able to consciously see stimuli in a particular region but can nevertheless perform visual discriminations (e.g. long, short) accurately
A region of extrastriate cortex associated with color perception
A region of extrastriate cortex associated with motion perception
A failure to perceive color (the world appears in grayscale), not to be confused with color blindness (deficient or absent types of cone cell)
A failure to perceive visual motion
In vision, a pathway extending from the occipital lobes to the temporal lobes involved in object recognition, memory, and semantics
In vision, a pathway extending from the occipital lobes to the parietal lobes involved in visually guided action and attention
The color of a surface is perceived as constant even when illuminated in different lighting conditions
The ability to detect whether a stimulus is animate or not from movement cues alone
A memory representation of the three-dimensional structure of objects
A failure to understand the meaning of objects due to a deficit at the level of object perception
A failure to understand the meaning of objects due to a deficit at the level of semantic memory
The process of segmenting a visual display into objects versus background surfaces
Figure–ground segregation
A failure to integrate parts into wholes in visual perception
An understanding that objects remain the same, irrespective of differences in viewing condition
A reduced neural response to a stimulus, or stimulus feature, that is repeated
Adaptation (or repetition suppression)
The notion that the brain represents different categories in different ways (and/or different regions)
Stored knowledge of the three-dimensional structure of familiar faces
Face recognition units (FRUs)
An abstract description of people that links together perceptual knowledge (e.g. faces) with semantic knowledge
Person identity nodes (PINs)
An area in the inferior temporal lobes that responds more to faces than other visual objects, and is implicated in processing facial identity
Impairments of face processing that do not reflect difficulties in early visual analysis (also used to refer to an inability to recognize previously familiar faces)
The tendency to perceive ambiguous or hybrid stimuli as either one thing or the other (rather than as both simultaneously or as a blend)
An inability to create mental images (unable to see with the minds eye)
A region of the visual ventral stream that responds more to scenes than objects
Parahippocampal place area (PPA)
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Useful Links
Learn more about visual illusions and how they are created by the brain: www.illusionoftheyear.com/
Do you think you have developmental (or congenital) prosopagnosia? www.troublewithfaces.org/
Or perhaps you never forget a face and could be a super-recognizer? http://superrecognisers.com/
This website has many fun visual illusions and has the added benefit of including a scientific explanation of them: www.michaelbach.de/ot/
