N165 Quiz 2; Unit 2c

The first stage in the functioning of the senses, starting with information at the peripheral sensory receptors

the process of recognizing, organizing, and interpreting sensory information

• made up of multiple visual areas, it is one of two main visual processing streams after primary visual cortex
• this pathway is involved in perception for action

• made up of multiple visual areas, it is one of two main visual processing streams after primary visual cortex
• this pathway is involved in perception for recognition

a property of sensory and motor systems in which one part of a topographical representation is relatively larger than the rest, producing a region with higher acuity (better sensitivity) in the magnified region. In the visual system, cortical magnification describes how many neurons in an area of the visual cortex are 'responsible' for processing a stimulus of a given size, as a function of visual field location. In the center of the visual field, corresponding to the center of the fovea of the retina, a very large number of neurons process information from a small region of the visual field. If the same stimulus is seen in the periphery of the visual field (i.e. away from the center), it would be processed by a much smaller number of neurons. The increased number of neurons devoted to processing central vision helps make our central vision more sensitive than our peripheral vision. The magnification of central (e.g., foveal) is achieved in several steps along the visual pathway, starting in the fovea with densely packed cones and the midget retinal ganglion cells of the parvocellular pathway and continuing to the large region of cortex that receives information from the central vision. Other examples of cortical magnification include the expansion of the face and hand representations in the somatosensory and motor cortical regions. These body parts have sensitive touch and excellent motor control.

a phenomenon where people who are perceptually blind demonstrate some response to virtual stimuli (because only part of their visual system is impaired, other parts- parts involved in motion perception- may still function)

• a disorder in which the patient suffers from the inability to recognize and identify objects, features of objects or scenes, faces or persons despite having knowledge of the characteristics of the objects, scenes, faces or persons.
• the condition can be loosely divided into two types that differ by severity: apperceptive and associative

• a disorder characterized by the inability to name, copy or recognize visually presented objects
• shape perception and figure-ground segregation is impaired, but basic visual functions (color discrimination, luminance discrimination, visual activity), and object identification based on non-visual cues are preserved.

• a disorder in which visual object recognition is impaired
• (ex. naming of visually presented objects, categorization, matching by function), but elementary visual perception is more or less preserved.
• this is how object agnosia is typically described, as this is the more common type.

• a disorder in which visual object recognition is impaired
• (ex. naming of visually presented objects, categorization, matching by function), but elementary visual perception is more or less preserved.
• ex. matching and copying of visually presented forms and objects, drawing from memory, and non-visual object recognition.

• a bilateral visual processing area that is thought to be specialized for face processing (with some controversy-- some authors argue that it is specialized for detailed visuospatial processing, not necessarily just face processing)
• damage to this region can cause face perception deficits

A disorder in which faces cannot be recognized, but other forms of object recognition are unimpaired

problems with recognizing a face vs. other objects (can't tell by vision alone whether something is a face or not)

problems with recognizing familiar faces (can tell it's a face, but not whose face it is)

• the delusional belief that an acquaintance has been replaced by an identical-looking imposter
• it is one of the delusional misidentification syndrome more commonly seen in schizophrenia, dementia, and brain trauma.
• may arise from an abnormal emotional response to faces --> disconnect between temporal and limbic cortex; possible example of a really high-order face processing issue.

• The delusional belief that different people are in fact a single person who changes appearance or is in disguise, generally viewed with paranoia (that the "shapeshifting" person is out to get them).
• This is another rare delusional misidentification syndrome.
• Appears to arise from damage to left frontal and right temporoparietal regions, possibly due to a disconnection between hemispheres, that affects high-order face processing.
• A person with the Fregoli delusion may also inaccurately recall places, objects, and events, leading to the theory that associations among stored memories may be messed up – with the image of one face (or place/object/event) ending up being improperly associated with another one.

• a deficit in scene perception, with a normal visual fields and normal lower-level (elementary) visual perception.
• Several theories have been proposed to account for simultagnosic symptoms: some focus on the disruption of a specific process, such as the speed of attentional processing, others focus on the disruption of a representational structure

a deficit in scene perception where the patient can only perceive one stimulus at a time (more severe than ventral type)

a deficit in scene perception where the patient can see multiple objects, but cannot recognize them (can navigate and count, but cannot read)

• an impairment of color vision in the entire visual field that arises from cortical lesions on the ventral surface of the temporal-occipital lobes.
• Loss of color vision in the full visual field is rare, as lesions would need to affect color processing in both hemispheres.

• Loss of color vision is restricted to one half of the visual field
• the rest of the virtual field has normal color vision
• (color vision can even be lost for just one quarter of the visual field)

temporary loss of color vision in any part of the visual field, usually from a TIA (transient ischemic attack)

• the inability to perceive motion that arises from damage to V5-MT- the area of cortex responsible for visual motion
• patients experience a strobe-light effect of vision
• it can be caused by damage such as stroke, trauma, and rarely from some antidepressants