What does wavelength play an important role in?
the perception of colour
What does intensity play an important role in?
the perception of brightness
Convergence
eyes turn inwards slightly; greatest when inspecting close up
Binocular disparity
difference in the position of the same image on two retinas; greater for close objects; depth perception cue
Duplexity theory
cones and rods mediate different kinds of vision
Photopic vision
cone-mediated; predominates in good lighting; high-acuity; coloured perceptions
Scotopic vision
rod-mediated; lacks detail and colour; predominates in dim light
Retina-geniculate-striate system
all signals from the left visual field reach the right primary visual cortex AND all signals from the right visual field reach the left primary visual cortex
Two parallel channels of communication flow that run through each lateral geniculate nucleus
- Parvocellular
2. Magnocellular
On-center cells
Respond to lights shone in the central region of their receptive fields with “on” firing AND to lights shone in the periphery of their receptive fields with inhibition followed by “off” firing when light is turned off
Off-center cells
Opposite of on-center cells
Respond with inhibition and “off” firing in response to lights in the center of their receptive fields AND with “on” firing to lights in the periphery of their receptive fields
Simple cortical cells
Receptive fields are divided into static “on” and “off” regions…
All monocular…
Respond best to straight-line stimuli in a specific orientation…
Receptive fields are rectangular
Complex cortical cells
Larger receptive fields... Not divided into “on” “off” regions... Many are binocular (respond to stimulation of either eye)... Can respond to movement... Respond best to straight line stimuli... Rectangular receptive fields
Component theory (aka trichromatic theory)
3 different kinds of colour receptors (cones);
Some are sensitive to short wavelengths, some to medium, some to long;
Came from idea that any colour can be made by mixing together of three different wavelengths
Opponent-process theory
Came from idea that complementary colours cannot exist together & afterimage;
Two different classes of cells in the visual system for encoding colour and another for encoding brightness
Blindsight
ability to respond to visual stimuli in a scotoma (area of blindness) with no conscious awareness of them
Dorsal stream
respond to spatial stimuli;
“Where” objects;
“Control of behaviour” - directs behavioural interactions with objects
Ventral stream
respond to characteristics of objects;
“What” objects;
“Conscious perception” - mediates the conscious perception of objects
Prosopagnosia
visual agnosia for faces
Ocular dominance columns
inputs carrying information from the left and right eye are initially kept separate in the primary visual cortex
Ex; A light shone in the left eye will fire off neurons in the left-eye ocular dominance columns but not in the right-eye ocular dominance columns and vice versa
Orientation columns
small chunks of primary visual cortex that have the same orientation preference
“Blobs”
in center of the ocular dominance columns - contain neurons responsive to colour
Ocular dominance plasticity
Occurs most readily in critical period and refers to the shift in ocular dominance
Ex; when one eye is not fully functional and more parts of the primary visual cortex start to respond to the other
Amblyopia
impairment of the visual cortex to process information
Binding problem
how does the brain bind together activity in widely distributed cortical areas into one perceptual conscious image?
Primary sensory cortex
input is mostly contralateral; receives input from the thalamic relay nuclei
Secondary sensory cortex
input is from both sides of body; receives input from primary sensory cortex or other areas of secondary sensory cortex
Association cortex
prefrontal and posterior parietal cortex (contains bimodal neurons); receives input from more than one sensory system
Fourier analysis
mathematical procedure for breaking down complex waves into their component sine waves
Missing fundamental
the pitch of a complex sound may not be directly related to the frequency of any of the sound’s components
The auditory system is largely ___________
tonotopic
Anterior auditory pathway
involved in identifying sounds; “what”
Posterior auditory pathway
involved in location sounds; “where”
Two major somatosensory pathways:
- Dorsal-column medial-lemniscus system
2. Anterolateral system
Anterolateral system
tends to carry information about pain & temperature
Dorsal-column medial-lemniscus system
tends to carry information about touch & proprioception (awareness of position & movement of body)
The human primary somatosensory cortex is _____________
somatotopic
Astereognosia
inability to recognize objects by touch
Asomatognosia
failure to recognize parts of one’s own body
- Usually unilateral (affecting only left side of body)
- Associated with damage to the right temporal and posterior parietal lobe
- Commonly a component of contralateral neglect
Anterior cingulate cortex
most frequently linked to pain
Descending pain control
pain can be suppressed by cognitive & emotional factors
Cross modal perception
Perception resulting from interactions between two or more sensory modalities
The angular gyrus
particularly important for sensory integration across modalities and cross modal perception
Synesthesia
A perceptual phenomenon in which stimulation of one sensory modality elicits a simultaneous and involuntary perceptual experience within another sensory modality
Most well researched form: grapheme-color synesthesia
In the sensory systems, information mainly flows up through the hierarchy, whereas in the sensorimotor system, information flows _______
down
Ballistic movements
Brief, “all-or-none”, high-speed movements that are not normally influenced by sensory feedback
Sensorimotor association cortex consists of two major areas:
- Posterior parietal association cortex
2. Dorsolateral prefrontal association cortex
Posterior parietal association cortex
Involved in perception of spatial location and guidance of voluntary behaviour
Associated with apraxia and contralateral neglect
Apraxia
disorder of voluntary movement, difficult making specific movements when requested to do so, but can do so unconsciously
Contralateral neglect
Inability to respond to stimuli on the side of the body opposite (contralateral) to the side of a brain lesion
Dorsolateral prefrontal association cortex
Involved in evaluation of external stimuli and decision to initiate complex voluntary motor responses
Secondary motor cortex
Thought to be involved in the programming of specific patterns of movements
Mirror neurons
Fire when an individual performs a goal-oriented movement or when they observe the same goal-oriented movement
First discovered in monkeys and provide a possible mechanism for social cognition
Primary motor cortex
Each site in the primary motor cortex receives sensory feedback from receptors in the muscles and joints that the site influences
Major point of convergence of cortical sensorimotor signals
Two important sensorimotor structures that interact with different levels of the hierarchy and coordinate & modulate its activities:
- Cerebellum
2. Basal ganglia
Cerebellum
Contains more than half of the brain’s neurons
Thought to correct ongoing movements that deviate from their intended course
Believed to play a major role in motor learning - sequences of movements
Basal ganglia
play a role in the modulation of motor output, like the cerebellum
Thought to also be involved in a variety of cognitive function (i.e., habit learning)
Dorsolateral motor pathways
Motor neurons activated project to distal muscles (i.e., finger muscles)
Ventromedial motor pathways
Motor neurons activated project to proximal muscles of the trunk and limbs (i.e., shoulders)
Fast muscle fibers
have few blood vessels (more pale)
Slow muscle fibers
have more blood vessels (more red)
Case of H.M.
Removal of medial portions of temporal lobes (including most of hippocampus & amygdala) to treat epilepsy
Treatment was called a bilateral medial temporal lobectomy
Led to the discovery of two categories of long term memory: explicit & implicit
Lost almost total ability to form new long-term memories -tests demonstrated that he had intact implicit memory
Intact short-term memory and intact remote, long-term memory
Explicit memory
conscious long-term memories
Implicit memory
long-term memory without conscious awareness
Major structures of the medial temporal lobes:
- Hippocampus
- Amygdala
- Medial temporal cortex
- CA1 subfield (in hippocampus)
Repetition priming tests assess…
implicit memory
Explicit long-term memories fall into two categories:
- Episodic
2. Semantic
Episodic memory
explicit memories for particular events of one’s life
Aka autobiographical memory
Semantic memory
explicit memories for general facts or information
Korsakoff’s syndrome
Disorder of memory common in people who have consumed large amounts of alcohol;
Attributable to brain damage associated with thiamine deficiency;
Characterized by a variety of sensory and motor problems (i.e., extreme confusion, personality changes, etc.)
Hebb’s theory of memory consolidation
Memories of experiences are stored in the short-term by neural activity circulating in closed circuits
Theses circulating patterns are susceptible to disruption but eventually they induce structural changes in the involved synapses which provide stable long-term storage
Reconsolidation
each time a memory is retrieved from long-term it is temporarily unstable in short-term memory, until it is reconsolidated
Delayed nonmatching-to-sampling test
Used with rats and monkeys;
Provided a means of testing the assumption that the amnesia resulting from medial temporal lobe damage is entirely the consequence of hippocampal damage
Radial arm maze and Morris water maze
Demonstrated that the hippocampus plays a role in spatial processing
Jennifer Aniston cells (aka concept cells)
found in the medial temporal lobe, respond to ideas of concepts (highly selective & invariant)
Infereotemporal cortex & memory
important role in storing memories of visual input
Amygdala & memory
memory for emotional significance of experiences
Prefrontal cortex & memory
plays a role in memory for tasks that involve a series of responses
Cerebellum & memory
plays a role in memory of learned sensorimotor skills
Striatum & memory
plays a role in habit formation memory (memory that develops over many trials)
Altering memories in PTSD patients
Reduce fear/stress associated with traumatic memories;
Trigger recall of memory to put it in an unstable state;
Administer drug that will blunt the hormonal and autonomic response to reliving the emotional experience
Engram
brain cells that are altered in some way after learning
Hebbian learning rule essentially says…
- Neurons that fire together wire together; neurons that are out of sync lose their link
- Neurons that are active together increase the strength of their synapses
- Neurons that reactivate together form cell assemblies
Cell assembly
Theoretical memory mechanism;
Groups of neurons that serve a common function such as forming and storing a memory;
Reactivation of the cell assembly allows the conscious recall of the memory
Long-term potentiation, aka LTP
high probability of concurrent pre and postsynaptic activity (synaptic strengthening)
the enduring facilitation of synaptic transmission that occurs following activation of synapses by high-intensity, high-frequency stimulation of presynaptic neurons
Long-term depression, aka LTD
low probability of concurrent pre and postsynaptic activity (synaptic weakening)
opposite of LTP and occurs in response to prolonged low-frequency stimulation of presynaptic neurons
LTP only develops if…
the firing of the presynaptic neuron is followed by the firing of the postsynaptic neuron
The co-occurrence of firing in presynaptic and postsynaptic cells is recognized as the __________ ______ in LTP
critical factor
Hebb’s postulate for learning
assumption that co-occurrence is a physiological necessity for learning and memory
The _____ receptor is prominent at the synapses at which LTP is commonly studied
NMDA
Metaplasticity
refers to the fact that LTP and/or LTD induction can be modulated by prior synaptic activity