Perception and Attention Flashcards
What wavelength can we view light?
400-700mm
Range
The range of what we can perceive
Acuity
How well we distinguish amon stimuli
Where do we have the best acuity and why?
The centre of the eye as the fovea is located here which has the most photoreceptors (cones)
Saccades
Rapid Eye Movements
Where do all sensory systems lead to?
The Thalamus
Inferior colliculus
Book definition: “A part of the midbrain that is involved in auditory processing. Compare superior colliculus. (p. 169)”
Interaural time (difference)
Book definition: “The difference in time between when a sound reaches each of the two ears. This information is represented at various stages in the auditory pathway and provides an important cue for sound localization. (p. 171)”
If a sound reaches your right ear before your left ear, the difference in timing will provide information about the sound’s location (in this case, somewhere on your right).
This is also the reason why we repeatedly turn our heads when trying to locate the source of a sound, using a mix of sound intensity and interaural time difference to help us.
Lateral geniculate nucleus (LGN)
Book definition: “The thalamic nucleus that is the main target of axons of the optic tract. Output from the LGN is directed primarily to the primary visual cortex (Brodmann area 17). Compare medial geniculate nucleus. (p. 187)”
The lateral geniculate nucleus, located in the thalamus, receives visual information transmitted from the retina through the optic nerve in the retinogeniculate pathway. As the optic nerves cross in the optic chiasm, each LGN receives information from its contralateral retina.
The LGN then sends information on to the primary visual cortex (V1) via the geniculocortical pathway.
In addition, as the different nuclei of the thalamus are interconnected, visual information can be connected to auditory information, and so on. This provides an opportunity for multisensory integration, e.g. integrating the visual input of someone’s lips moving with the auditory input of their voice.
Medial geniculate nucleus (MGN)
Book definition: “A collection of cell bodies in the medial portion of the thalamus involved in processing auditory information. Output from the MGN is directed primarily to the primary auditory cortex. Compare lateral geniculate nucleus (LGN) (p. 167)”
In addition to output from the MGN to the primary auditory cortex A1, the different nuclei of the thalamus are also interconnected, meaning that auditory information can be connected to visual information, and so on. This provides an opportunity for multisensory integration, e.g. integrating the auditory input of someone’s voice with the visual input of their lips moving.
What are rods?
Contain rhodopsin
-Most useful at night
-Pigment becomes depleted quickly in bright light
-Evenly distributed
What are cones?
Contains photopsin
-Replenish fast + require more instense light
-During day
-Three types of cones for colour
-More dense in fovea
How can rods amplify a dim light?
As there are many rods for each ganglion cell while the cone has as few as one. Low aquity tho as info cant be pinpointed to single rod
Info for where goes?
Along the DORSAL path from VI to the PARIETAL LOBE
Infor for what goes?
Along the VENTRAl path from VI to the temporal lobe
Where is the primary visual cortex?
Posterior occipital lobe
Akinetopsia
Book definition: “A selective disorder of motion perception resulting from a lesion or lesions of the central nervous system. Patients with akinetopsia fail to perceive stimulus movement, created by either a moving object or their own motion, in a smooth manner. In severe cases, the patient may only infer motion by noting that the position of objects in the environment has changed over time, as if the patient were constructing dynamics through a series of successive static snapshots. (p. 204)”
Akinetopsia has often been linked to lesions in the middle temporal visual area (area MT or V5), which is thought to be involved in motion perception.
The disorder can take on several forms. In inconspicuous akinetopsia, patients describe seeing motion as a lagging cinema reel or as a series of overlaid pictures. In the much rarer case of gross akinetopsia, no motion is perceived whatsoever, resulting in seeing the world as a series of still images.
A patient suffering from gross akinetopsia noted her difficulties in pouring a liquid into a cup, as the liquid would simply appear frozen in midair until suddenly, the cup had overflowed. She also noted feeling uncomfortable being in a room with multiple people, as people would seem to blip in and out of existence whenever they moved
Achromatopsia
Book definition: “A selective disorder of color perception resulting from a lesion or lesions of the central nervous system, typically in the ventral pathway of the visual cortex. In achromatopsia, the deficit in color perception is disproportionately greater than that associated with form perception. Colors, if perceived at all, tend to be muted. (p. 201)”
Achromatopsia is not to be confused with color-blindness.
In contrast, color-blindness is the result of a gene causing abnormalities in the photoreceptor system. Dichromatic color-blindness is caused by the lack of a third photopigment, while anomalous trichromatic color-blindness is caused by abnormal sensitivity in one of the three photopigments.
FFA
Fusiform Face Area, sensitve to faces in the fusiform gyrus
PPA
Parohippocampal Place Area which responds to objects more
Simultanagosia
Inability to perceive simultaneous events.
Cant see the big picture
Focuses on items only
Oculomotor Apraxia
Inability to guide the eye
Difficulty focusing eye and often moves head instead
Optic Ataxia
Cant move your hand towards an object using just visual info
Prosopagnosia
Difficulty recognising faces
Balints Syndrome
Trifecta of optica ataxia, oculomotro apraxia and simultanagosia
What causes balints syndrome
Bilateral damage to posterior parietal and occipital lobe
The superior colliculus (midbrain) and the pulvinar nucleus (thalamus)
Heavily involved in attention
What may cause ADHD
Anatomical differences in white matter in the attention network
Studies have found less white matter in prefrontal cortex in ADHD patients
Apperceptive Agnosia
You see a pile of lego instead of a building
-Unusual view test – Patients cannot recognise objects from different odd angles
-You lack a coherent percept of the world
-Difficulty naming objects
Integrative Agnosia
Difficulty integrating features into whole things
-at legoland they see doors and windows but not the house
-To recognise a dog they’d see legs and a tail before building up to a dog
Associative Visual Agnosia
Can perceive things but cant assign meaning to them
-Can perceive and draw a house but cant recognise it
-People have no issue recognising faces
Matching by Function test
Tests patients to match objects by function. People with associative visual agnosia would struggle especially those with left hemisphere damage
Cogenitial Prosopagnosia
Lifetime impairment in facial recognition with no neurological cause
-No issue with objects
-Normal FFA activation
- One study found reduced activity between FFA and RIGHT ANTERIOR TEMPORAL region associated with faces
Shorter Wavelengths is for what colour
BLUE
Medium Wavelengths are for what colour
GREEN
Longer wavelengths are for what colour?
RED
Objects in the left visual field stimulate?
The nasal hemi-retina of the left eye
The lateral hemi-retina of the right eye
Objects in the right visual field stimulate?
The nasal-hemi retina of the right eye
The lateral hemi retina of the left eye
Which pathway contains 90% of axons in the optic nerve?
Retinogeniculate pathway
The remaining 10% of axons of the optic nerve fibers go through which other structueres?
Pulvinar nucleus of the thalamus
Superior Colliculus of the midbrain
V1 neurons are sensitive to?
Edges
V4 neurons are sensitive to?
Colour
V5 neurons are sensitive to?
Motion
P cells
Parvocellular Layers in the LGN, projects to the top four layers
They respond to colour, fine detail, still objects, slow moving objects
Smaller than M cells
M cells
Magnocellular Layers in the LGN project to the bottom two layers
They respond to fast moving things
Ventral Stream flows
Primary Visual Cortex
Ventral Prestriate Cortex
Inferotemporal Cortex
Dorsal Stream flows
Primary visual cortex
Dorsal prestriate cortex
Posterior Parietal cortex
