Perception and Neuropsychology Flashcards
Sensation
Process by which sense organs receive and transmit information
Perception
Brain’s processing and interpretation of information
Absolute threshold
Lowest intensity at which a stimulus is detected 50% of the time
Neural implementation
- Sensory organs absorb energy
- Energy is transduced into a neural signal
- The neural signal is sent throughout the brain, where further processing takes place
Cornea
Outer area of the eye, focuses the image
Choroid
Middle area of the eye, transports waste away from the eye
Iris
Inner area of the eye, controls the pupil; amount of light let in
Lens
Inner part of the eye, focuses image onto the back of the retina; contracts and expands as needed to look close or far away
Congenital cataracts (born with cataracts)
Even after removing faulty cataracts, people remain blind (critical period for vision)
Vitreous humor
Inner part of eye, provides nutrients and removes waste
Retina
Inner part of eye, transduces electromagnetic energy into a neural signal
Cones (photoreceptors)
High-resolution system, daytime, found on the fovea
Rods (photoreceptors)
Low-resolution system, nighttime, situated peripherally; MORE NUMEROUS THAN CONES AND MORE SENSITIVE TO LIGHT !!
Gyrus
Ridge on the surface of the brain, surrounded by fissures known as ‘sulci’
Occipital lobe and vision
Serves one sensory modality (vision), while frontal, temporal, and parietal lobes are all multi-modal
Mishkin & Undergleider 1982
Double dissociation; temporal lobe damage resulted in impaired object discrimination, while parietal lobe damage resulted in impaired landmark discrimination
Ventral stream pattern perception
Lets you know what things are
Dorsal stream spatial location
Where things are
Parietal lobe
Helps us orientate ourselves
Temporal lobe
Helps us to interpret information
What activates retinal ganglion cells?
Spots of light or dark maximally activate the retinal ganglion cells
Lateral geniculate nucleus (LGN cells) are activated by:
Spots of light
What activates V1 cells?
Lines activate V1 cells
What activates beyond V1 (far reaches of the ventral visual stream)?
Jagged features
Area TE/IT (situated in far reaches of visual system) is activated by…?
Activated by facial profiles, processes complex features
Retinotopic mapping
Point-to-point mapping of the external world onto the retina, lateral geniculate nucleus, and V1 (cells have a highly specific function that they do not work outside of); NO retinotopic mapping beyond V1 !!
Where in the visual system is retinotopic mapping present?
Before and in V1
Receptive field of the retina
Area of the retina which, when stimulated by light, causes a change in the neural activity of the cell
Centre-surround architecture
Enhances contrast/ view of image
Lateral inhibition
Visual process in which the firing of a retinal cell inhibits the firing of surrounding retinal cells
Temporal retina
Temporal retina fibres come out of the eye and ‘swap’ sides (example: temporal retinal fibres of the left eye look at the right visual field)
Nasal retina
Fibres come out of the eye and ‘stay’ on their side (example: nasal retina fibres from the right eye look at the right visual field)
What side of the brain looks at the left visual fields of both eyes?
Right side
What side of the brain looks at the right visual fields of both eyes?
Left side
Right-monocular blindness
Result of a severed optic nerve of the right eye, blind in the right eye
Bitemporal hemianopia
Result of a severed optic chiasm, both outer temporal visual fields are damaged
Left-homonymous hemianopia
Result of severed optic track, blindness in both left fields; any cut after the optic chiasm and up to the primary visual cortex will cause left-homonymous hemianopia
What does damage to the primary visual cortex result in (vision)?
Left-homonymous hemianopia and macular sparing (central vision is spared)
Patient D.B. (blindsight)
5% of visual information goes directly from the eyes to the dorsal pathway on the way to the parietal lobe; this is why D.B. can tell you where something is, although he cannot identify what the object is
Area V5
Visual motion area (function of cells in that area is to tell the next station in the visual system that something is moving)
Achromatopsia
Absence of colour vision, occurs as a result of damage to V4 (involved in colour perception and situated laterally on the outside area of the cortex) and nothing else
Akinetopsia
Absence of motion vision, occurs as a result of damage to V5
Visual agnosia
Inability to identify an object
Apperceptive agnosia
Failure of object recognition due to a failure of visual perception, due to partial damage to occipital lobe; associated with scotomas
Scotomas
Series of small blindspots; viewing the world through a ‘peppery mask’
Dorsal simultagnosia
Failure of object recognition due to a spatial perceptual impairment (can recognise objects, but not more than one at a time - CANNOT see multiple objects), occurs due to damage to the parietal lobe
Ventral simultagnosia
Failure of object recognition due to a complex perceptual impairment (beyond V1); can recognise objects but not more than one at a time, BUT can see multiple objects
Associative agnosia
Difficulty understanding the meaning of what you are seeing, occurs due to damage beyond V1
Bottom-up theory
When you look at an object, you break the object down into its constituent parts and then build it back up to gain recognition of what the object is
Top-down theory
See bigger picture and then ‘hypothesis test’
Depth perception: Binocular clues
We have two forward-facing eyes (the visual fields of the eyes often overlap); convergence (eyes moving closer together as the object of interest moves closer); binocular disparity (two eyes see different things)
Motion parallax
Things that are closer to the viewer appear to be moving faster
Relative height/ location
Things that are closer to the horizon tend to be further away from you
Linear perspective
As two parallel lines get further away, they get closer together
Interposition
An object that overlaps another is perceived to be closer to the viewer
Texture gradient
Texture gradient will appear denser as it gets further away
Relative size
Objects that are close to viewer appear larger, objects that are farther away appear smaller
Depth perception: Monocular clues
Can be seen in a still image (relative size, texture gradients, interposition, perspective, relative height = ‘pictorial’ depth cues); motion parallax (things that are closer to us appear to be moving faster)
Perceptual constancies
Our perception of a familiar object stays constant, even when the object’s retinal image changes
Size constancy
When an object’s retinal image size changes due to distance, but our perception of the object’s size remains the same
Subjective contours
Perceived contours/ edges where there is no physical contour in the image
Ponzo illusion
Top object perceived as larger than bottom one, even though they are both the same size (to do with background: converging lines)
Young-Helmholtz trichromatic theory
Short wavelength cones sensitive to blues, medium wavelength cones sensitive to greens/ yellows, and long wave-length cones that are more sensitive to reds; doesn’t explain why colour blindness occurs in pairs or why you get colour after-effects
Opponent-process theory
Occurs just beyond the cones in the retina, in the bipolar and ganglion cells; you might have a blue-yellow opponent cell (retinal ganglion cell that fires more to blue and fires less to yellow, or that does the opposite; responses occur as a pair)
René Descartes
First person to attempt to localise brain function
Gall & Spurzheim (1800s): Phrenology
Correlated bumps and depressions on the skull with certain faculties
Broca & Patient Tan 1861
Left-frontal lobe of the brain known as Broca’s area and damage to it results in Broca’s aphasia (difficulty with the motor aspects of speech)
Wernicke 1874
Damage to the left-temporal area of the brain (Wernicke’s area) results in Wernicke’s aphasia - affected individuals can speak normally, but struggle to comprehend speech
Fritsch & Hitzig 1870
Discovered that the brain is an electrical structure
Key anatomy of the temporal lobe
- Lateral surface (superior, middle, and inferior temporal gyrus; known collectively as the ‘visual ventral stream’), medial surface (medial temporal lobe)
- Middle and inferior temporal gyrus make up the ventral stream
- Superior temporal gyrus is all auditory (auditory cortical region of the brain)
- Medial temporal lobe (cortical tissue that’s wrapped up around the inside of the brain)
Damage to right-medial temporal lobe results in…
Visual memory impairments
Damage to left-medial temporal lobe results in…
Impaired verbal memory
Patient H.M. and multiple memory systems
Skill-learning remains intact for individuals with damage to the medial temporal lobe, supports multiple memory systems theory: declarative memory affected by damage to the area, while non-declarative memory is spared despite damage to the area
Patient H.M. and memory consolidation
Found that memory is not stored in the medial temporal lobe; rather, the medial temporal lobe is responsible for consolidating memories in your brain
Effects of damage to the parietal lobe:
Impairments in processing spatial information:
1. Impairments in integrating sensory information
2. Impairments in the control of movement
3. Impairments in guiding movements to points in space
4. Impairments in abstract concepts
5. Impairments in directing attention
Effects of left-parietal damage:
- Agraphia (difficulty writing)
- Acalculia (difficulty organising information spatially)
- Right/ left confusion
- Dyslexia (difficulties with reading, etc.)
- Difficulty drawing details
Effects of right-parietal damage:
- Difficulty in recognising unfamiliar views of objects
- Difficulty in drawing (overall shape)
- Contralateral neglect (damage to the right parietal lobe → neglect the left)
Is contralateral neglect perceptual or post-perceptual?
Information is getting in, just not being acknowledged (post-perceptual rather than perceptual)
Ego-centred neglect
Neglect the a certain side of something in relation to the body’s axis
Object-centred neglect
Body axis does not matter; certain side of object is neglected, regardless of where the individual’s body is
Driver et al. 1994
Found that there was an object-based component to neglect
Damage to motor and premotor cortex results in:
- Loss of fine movements, strength, and speed
- Broca’s aphasia
Word fluency test
Found that individuals with a damaged prefrontal cortex had reduced output in the test (loss of divergent thinking)
Divergent thinking
Process of creating multiple solutions/ approaches to a problem
Convergent thinking
Finds one well-defined solution to a problem
Damage to the frontal lobe (prefrontal cortex):
- Does not impair convergent thinking
- DOES impair divergent thinking
- Impaired response inhibition
Wisconsin card sorting test (impairments in response inhibition)
Individuals without prefrontal cortex damage quickly adapt, while individuals with prefrontal cortex damage continue to repeat previously rewarded behaviour, despite being consistently told that their responses are wrong
Stroop interference test
Impacted individuals with prefrontal cortex damage more than those without
Lhermitte (1983, 1985): Environmental dependency syndrome
Individuals with prefrontal cortex damage use the objects for intended purpose, regardless of context
Phinneas Gage
Severed optic nerve and acquired damage to frontal lobe; personality changed and executive function was damaged
Sound waves
Variations in the density (pressure) of air
Amplitude
Vertical size of the sound waves; that is, the amount of compression and expansion of the molecules in the conducting medium
How is sound processed in the ear?
- Soundwaves travel through auditory canal to the eardrum (tympanic membrane)
- Soundwaves vibrate eardrum → vibrations are sent to three tiny bones (ossicles) in the middle ear and amplified
- Amplified vibrations sent to cochlea in the inner ear (divided by basilar membrane and containing thousands of tiny hair cells that function as sound receptors)
- When sound waves strike eardrum, fluid inside cochlea is set into motion → bending of hair cells triggering the release of NTs into the synaptic space between the hair cells and the neurons of the auditory nerve → nerve impulses sent to the temporal lobe’s auditory cortex
Loudness
Coded by both the rate of firing in the axons of the auditory nerve and the specific hair cells that are sending messages
Theories for how pitch is encoded:
- Frequency theory, in which the firing rate of the fibres matches the frequency of the sound waves being encoded
- Place theory, in which cells in particular locations in the cochlea encode specific frequencies
Conduction deafness
Results from damage to the structures in the ear that impairs the conduction of sound waves to the cochlea
Nerve deafness
Caused by damage to the receptors in the cochlea or auditory nerve
How does the visual system carry out sensation and perception?
All of the visual system carries out sensation and perception, but early on in the system is largely sensation while later on is more perception
How does light flow through the eye?
From the ganglion cell layer to the bipolar cell layer, to the photoreceptor layer
How are images processed from the eye to beyond?
Fibres come out of the eye and go to the lateral geniculate nucleus (situated in ventral and dorsal streams) –> go from there to V1 (primary visual cortex)
Hermann grid illusion
Illusion causes viewer to see black dots because in the fovea, cells are packed more tightly (entire receptive field falls inside the centre of ‘centre and surround’) –> when foveating, there is no distinction between centre and surround; evidence for lateral inhibition
Damage to primary auditory cortex (A1) on the superior temporal gyrus results in:
Deafness, and in certain cases deaf hearing, auditory agnosia (inability to recognise/ differentiate between sounds) and Wernicke’s aphasia (inability to interpret sounds)
Damage to superior temporal gyri results in:
- Deafness (bilateral damage to A1)
- Auditory agnosia
- Wernicke’s aphasia
Damage to middle and inferior temporal gyri results in:
- Achromatopsia
- Akinetopsia
- Ventral simultagnosia
- Associative agnosia
Complete damage to occipital lobe results in:
Blindness and blindsight
Partial damage to occipital lobe results in:
Apperceptive agnosia
