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Biopsych - Sensory Systems (Y1) - Coggle Diagram
Biopsych - Sensory Systems (Y1)
Auditory systems
Sound perception system - vibrations of air molecules that stimulate the auditory system
Pure tones only exist in labs - in real life, tones are always complex, and the auditory system breaks it down (Fourier analysis)
Close relationship between the frequency of the tone and its perceived pitch, pitch related to fundamental frequency (highest divisor for component frequencies)
Pitch complex sound may not be directly related to the frequency of any of the sound's components (200,300 and 400 would have pitch of 100 as this is highest divisor)
The Ear - soundwaves travel from outer ear down the auditory canal, causing eardrum to vibrate
Vibrations transferred to ossicles (small bones in the middle ear, malleus - hammer, incus - anvil, stapes - stirrups)
Vibrations in stapes trigger vibration of the oval windown which transfers to cochlea
internal structure of Cochlea is Organ of Corti
Organ of corti - basilar membrance and tectorial membrane
Hair cells - basilar membrane mounted here, tectorial membrane rests on them
A deflection of the organ of corti at any point along its length produces a shearing force on the hair cells, stimulating them and increasing the firing of axons in the auditory nerve - branch of auditory-vestibular nerve
Vibrations of the cochlear fluid are dissipated by the round window, which is an elastic membrane in the cochlear wall
Cochlea is very sensitive - major principle of coding is that different frequencies produce maximal stimulation of hair cells at different points along the basilar membrane - higher frequencies produce greater activation closer to windows and tip of basilar membrane
Many component frequencies that make up each complex sound activate hair cells across different points on the membrane
Tonotopic organisation - organisation by frequency
Ability to not get overwhelmed by amount of sounds and still independently understand each one has not been determined but the mechanism is theorised to be due to the synchronous relationship over time of the frequency elements of each sound source
Semicircular canals - receptive organs of vestibular system, which carries information about the direction and intensity of head movements, allowing us to maintain balance
From the Ear to the Primary Auditory cortex - network of auditory pathways, axon of each auditory nerve synapse in the ipsilateral cochlear nuclei from which many projections leading to superior olives on both sides of the brain stem
Axons in the olivery neurons project via the lateral lemniscus to the inferior colliculi where they synapse onto neurons that project to the medial geniculate nuclei of the thalamus project to the primary auditory cortex
Located in the temporal lobe - primary auditory cortex has three adjacent areas - core region
Surrounding the core region is a band / belt of areas of the secondary cortex areas outside of this are known as the parabelt area, 13 separate areas of auditory cortex
Organised into functional columns like the visual system (organised by frequency as it is tonotopic)
Sensitive to fluctuations known as periodotopy
Use natural sounds to test auditory cortex as pure sounds lack ecological validity
Auditory cortex does not produce signals that are faithful representations of sounds, but rather integrates information about current perceptions and behaviours to make auditory signals relevant to the animals current situation
Two streams of auditory cortex - auditory signals are conducted to the prefrontal and posterio parietal cortex
Anterior auditory pathway - what sounds are
Posterior auditory pathway - where sounds are
Auditory visual interactions - association cortex is usually defined as areas of cortex where such interactions as these take place - posterior parietal neurons found to have visual receptive fields, and some were found to have auditory receptive fields, and some have both
Studied through fMRI - sensory interaction seems to be an early and integral part of sensory processing
Perception of pitch - auditory neurons respond to frequency changes over pitch, Bendor and Wang (2005) studied monkey brains, fMRI found similar areas in the human brain which do this
Impact of damage - auditroy cortex damage leads to complete loss of hearing, loss of ability to process structural aspects of sounds, which is necessary for processing speech
Patients with damage to anterior auditory cortex will have trouble identifying sounds, and patients with damage to the posterior have trouble locating sounds
Deafness - 360 million people
Result from damage to inner or middle ear - two classes of hearing damage, either in ossicles (conductive deafness) and damage to the cochlea or auditory nerve (nerve deafness) - major cause of nerve deafness is losing hair cell receptors
Cochlea damage leads to difficulty distinguishing sounds
Hearing loss also associated with tinnitus (ear ringing) - when one ear rings the damage is located here, but cutting the nerve has no effect on ringing, suggesting neuroplastic changes resulting from deafness cause this condition
Cochlear implants - bypass damage to auditory hair cells by converting sounds picked up by a microphone on the patient's ear to electrical signals which excites the auditory nerve
General principles of sensory systems
Reception of external signals - each system is specialized to analyse specific information from the environment
Vision - light waves
Audition - sound / pressure waves
Vestibular sense - movement of liquid, gravity
Olfactory sense - odours
Gustatory sense - taste
Body sense - pressure, vibration, skin damage (touch and pain), muscle, joint and skin movements (movement senses)
Range of sensory perception differs between animal species and humans e.g. human hearing frequency (dolphin can hear ultrasounds, elephants can hear infrasounds)
Every system has specific receptors to extract relevant information
Receptors have receptive fields
Sound reception - inner hair cells; mechanically gated TRPA1 channel (K+ enters endolymph on the reticular lamina, reaching the voltage gated calcium channel and causing depolarisation, allowing Ca2+ into the cell
-> Vesicles filled with an excitatory neurotransmitter then diffuse to the perilymph and spiral ganglion neurite, transmitting the neural signal of the sound - organ of Corti
Skin receptors - Mechanoreceptors - somatosensory reception - free nerve endings for temperature, pain, tickles and itches
Merkel's disks - very light touch
Free nerve ending associated with the root of a hair
Pacinian corpuscle - deeper pressure / vibration
Meissner's corpuscle - light touch e.g. rough surfaces
Ruffini corpuscle - sustained pressure, little adaptation
Sensitive to physical distortion - bending, stretching, pressure and vibration
Receptive fields - the receptive fields of the three primary sensory neurons overlap
Secondary receptive field includes the three overlapping primary receptive fields
Primary sensory neurons converge on one secondary sensory neuron
Secondary sensory neuron with large receptive field
Sends signal to brain through spinal cord
Touch adaptation - cease to feel top of socks - stops unecessary sensation
Receptors classified on morphology and also adaptive and receptive fields
Two point discrimination - fingertips are the most sensitive area of the body - high density of mechanoreceptors, and receptors with small receptive fields such as Merkel's disks are very sensitive - more brain tissue devoted to fingertips
Two main differences between mechanoreceptors - receptive field size and adaptation
Transduction - external signals are transformed into action potentials
Stimulus properties need to be coded by neurons (neural coding)
Rate coding - frequency or firing rate
Loudness of sound or light - more APs in one time suggests higher rate coding
Adaptation - reduction of neural activity over time when stimulus is constantly presented
System is often more interested in changes in the external world than in consistency, easily bored
Place coding - location of stimulus on skin
Labelled line coding - specific sensitivity - taste; specific receptors code for specific tastes (1-10 for sweet, 11-32 for salty and 33-40 for sour)
Different qualities you experience
However, receptors not specific enough to detect fine differences, solution of population coding
Population coding - multiple receptors
Activation of many neurons together determines the specific sensation - combination of receptors, cross sensory information is critical
Coding of termpoal patterns - phase locking -
High firing rate limited by refractory periods
At a high frequency, sound waves travel too fast for action potentials of individual neurons to accurately represent their timing e.g. auditory systems
Transmission - from neuron to cortex: receptor -> peripheral pathway -> thalamus -> primary sensory cortex -> secondary cortical area
Processing the information -
Tonotopy - columnar organisation of cells with similar binaural interaction - structure of A1 and secondary auditory areas
Homunculus - somatotopy - differences in acuity correspond to differences in the relative proportions of the somatosensory cortex devoted to analysing information from these body regions
Small receptive field = large cortical area
Bottom up and top down processes
Bottom up - extraction of stimulus features from data without prior knowledge / memory / attention
Top down - influence from higher levels of the nervous system to lower levels, with prior knowledge, memory and attention
Primary sensory cortex - receives input directly from thalamic relay nuceli of the system
Secondary sensory cortex receives input from primary cortex or other areas of the same system
Association cortex receives input from more than one sensory cortex
Organized by hierarchy - specificity and complexity increases as you ascend hierarchy
Apparent from effects of damage to various levels - higher level of damage = more complex deficit
Functional segregation - all three levels of cerebral cortex have distinct and specialised areas of analysis, not homogenous
Parallel processing - information flows through multiple pathways simultaneously, not sequentially, signal analysed in different ways by the multiple parallel pathways
Visual, or optical, illusions show us that our minds tend to make assumptions about the world - what you see is often not the truth
Herman grid illusion (areas look grey until you look at them, then they look white - intersections simply look grey) and Mach band illusion (contrast and share around grid makes colour look different)
How do we perceive our reality, and how much of the information that we receive actually matches the real world
As you move your eyes, your perception of reality changes
Somatosensory systems - touch and pain
Sensations on your body are referred to as somatosensation - somatosensory system mediates these bodily sensations -
Exteroceptive system; external stimuli applied to the skin- mechanical stimuli division, thermal stimuli division and nocicpetive stimuli (pain)
Proprioceptive system - monitors information about the position of the body that comes from receptors in the muscles, joints and organs of balance
Interoceptive system - provides general information about conditions within the body (temperature and blood pressure)
Cutaneous receptors - skin receptors: free nerve endings, Pacinian corpuscles, Merkel's disks, Ruffini endings
When constant pressure is applied to the skin, this evokes a burst of firing in all receptors which corresponds to the sensation of being touched - however, after 100 miliseonds, only the slowly adapting receptors remain active and sensation quality changes
Stereognosis (identifying objects by touch) - manipulate the object in your hands so that the pattern of stimulation continually changes - having some receptors that adapt quickly and some and some that adapt slowly provides information about dynamic and static qualities of tactual stimuli
Various receptors have the same function - stimuli on the skin deform or change the chemistry of the receptor, which changes the permeability of it to a certain ions - neural signal created
Each tactile sensation appears to be produced by the interaction of multiple receptor mechanisms, and each receptor mechanism contributes to multiple sensations
Skin cells around particular receptors also seem to play a role in the quality of sensations produced by that receptor
Two major somatosensory pathways -
dorsal column medial-lemniscus system
Information about touch and proprioception
Sensory neurons enter spinal cord through dorsal root, ascend ipsilaterally and synapse in the dorsal column nuclei of the medulla
Axons of these neurons then decussate - cross to other side and ascend the medial lemniscus to contralateral ventral posterior nucleus of the thalamus
Ventral posterior nuclei receive input from the branches of the trigeminal nerve, which carries somatosensory information from the contralateral areas of the face; most neurons of the ventral posterior nucleus project to the primary SC, and others project to the secondary of posterior parietal cortex
Anterolateral system - carries information about pain and temperature
Dorsal root neurons synapse as they enter spinal cord - axons of second order neurons decussate but then ascend to the brain in the contralateral anterolateral portion of the spinal cord - however, some ascend ipsilaterally
Spinothalamic tract (pain), spinoreticular tract, spinotectal tract - pain is different to touch due to nerve endings, connections in spinal cord and axon diameter
All of these carry pain and temperature information that reaches the thalamus and this is then distributed to the somatosensory cortex and other brain areas
Not completely separated pathways, and lesions to the DCML do not eliminate touch and perception, and lesions to the AS do not eliminate perception of pain and termperature
If both are transected by spinal injury, the patient cannot feel sensation from below the level of the cut
Cortical areas of somatosensation - Penfield (1937) - mapped somatosensory cortex by applying electrical stimulation to various sites of cortical surface and asking patients to describe what they felt
Postcentral gyrus - somatosensory sensations in various body parts
Mapped relation between each site of stimulation and the part of the body in which the sensation was felt, discovering that the human somatosensory cortex is somatotopic - organised according to a map of the body surface (homuculus)
Distorted - greatest proportion of SI is dedicated from receiving input from the parts of the body we use to make tactile discriminations; in contrast, only small areas of SI receive input from large areas of the body, as they usually make no somatosensory discriminations
Secondary somatosensory cortex (SII) - also organised like this, lies ventral to the SI in the postcentral gyrus and exntending into the lateral fissure
SII receives SI input - SI is largely contralateral in its input, whereas SII receives substantial input from both sides of the body
Most of the input of SI and SII goes to the association cortex of the posterior parietal lobe
Studies of single neurons in primary somatosensory cortex found evidence for columnar organisation (similar to auditory and visual cortexes) - each neuron in a column has a receptive field in the same part of the body and responds most robustly to the same type of tactile stimuli
SI has 4 functional strips - each have a similar, separate somatotopic organisation, and each is sensitive to a different kind of somatosensory input - prefer one of 4 types of tactile stimulation
Two streams of analysis - dorsal that projects to posterio parietal cortex and participants in multisensory integration and direction of attention, and a ventral stream that projects to the SII and participates in perception of object's shapes
Damage to somatosensory cortex results in remarkably mild effects - mainly due to it having multiple parallel pathways
Somatosensory agnosias:
Astereognosis - inability to recognise objects by touch; simple sensory deficits that cause pure cases of this are rare
Asomatognosia - failure to recognise part's of one's own body - usually unilateral on the left side of the body, due to extensive damage in the right temporal and posterior parietal lobe
Anosognosia - failure of neuropsychological patients to recognise their own symptoms
Commonly a component of contralateral neglect - tendency to not respond to stimuli that are contralateral to a right hemisphere injury
Somatosensory system and association cortex: ultimately conducted to the highest level of the sensory hierarchy, areas of the association cortex in prefrontal and posterior parietal cortex
Posterior parietal cortex contains bimodel neurons - some of these respond to somatosensory and visual stimuli as the receptive fields of each are spatially related - as left hand moves, the visual receptive field of the neuron moves with it, and if there is a somatosensory receptive field centered in the left hand, its visual field is adjacent
Rubber hand illusion -
Feeling that extraneous objects, in this case a rubber hand, is actually part of the body (in experiments conducted to test this, real hand is hidden and replaced with rubber hand which is stroked - report sensation and also temperature in hidden hand drops)
Association cortex in posterior parietal and frontal lobes play a role in its induction - bimodal neurons with both visual and somatosensory fields have a critical role
Perception of pain - it is adaptive; one paradox of pain is that it is an experience that seems in every respect to be so bad it is important for our survival - no special stimulus, but rather it is a response to any potentially harmful stimulation of any type - stops us engaging in risky activity and to seek treatment
Those who feel no pain - congenital insensitivity to pain
Genetic abnormality underlies this disorder - influences synthesis of sodium ion channels
Pain has no clear cortical representation - painful stimuli activate many areas of the cortex including the thalamus, SI and SII, the insula and the anterior cingulate cortex - none are necessary for pain perception
Even hemisphectorised patients can still perceive pain in both sides of the body
Anterior cingulate gyrus most linked to pain
Thermal grid illusion - perception of pain from placing one's hand on a grid of metal rods that alternate between cool and warm and in this illusion participants experienced illusory pain while undergoing fMRI, and only this area displayed an increase in activity
Pain is modulated by cognition and emotion - those in life and death situations often feel no pain until after the event has finished
Descending pain-control circuit - electrical stimulation of the periaqueductal grey (PAG) has an analgesic (pain-blocking effects) Reynolds (1969) performed surgery on rats with no analgesia other than PAG simtulation
PAG and other areas of the brain contain specialised receptors for opioid analgesic drugs
Isolation of several endogenous opioid analgesics - endorphins
These three findings suggest that analgesic drugs and psychological factors might block pain through endorphin-sensitive circuit that descends from the PAG
Output of the PAG excites the serotonergic neurons of the raphe nucleus which project down the dorsal columns of the spinal cord and excite interneurons that block incoming pain signals in the dorsal horn
Basbaum and Fields (1978) - both anterior cingulate and prefrontal cortex are believed to be important components of descending analgesia circuits
Gate theory - neurons are excitatory to both sensory and pain axons
Neuropathic pain - severe chronic pain in the absence of recognisable pain stimulus - usually develops after injury has healed; attacks of this can be triggered by an innocuous stimulus, such as gentle touch
Can be associated with phantom limb syndrome
Microglial activity has been linked to the induction of neuroplastic changes that lead to the persistence of pain long after it has healed
Epigenetic mechanisms in neuropathic pain - drugs being developed to modify changes in order to treat them
Neuroplastic and epigenetic changes are most prominent in the anterior cingulate cortex - involved in descending analgesic pathway (if stopped, phantom pain continues)
Phantom limb syndrome
Impact on the somatotopic map - areas involved in the sensation for the limb lost still remain active, as the nerves believe that the limb is still there even when it is not
The mind constructs pain which causes the individual to think about the pain they feel, and this then increases the pain further
Brain has a complete map of each side of the body to the opposite side of the brain - left somatosensory cortex mirrors sensation of the right side of the body - each point of the body surface has a corresponding place on the cortex; hand and face are close together, and so phantom limb syndrome is the signals being confused (sensation in the face causes sensation in the hand)
Part of brain corresponding to the hand no longer has sensory input, and so the facial area extends into the atrophied hand section and takes over sensation, explaining why the two areas are now linked in sensation
Not logically ordered
Brain plasticity
fMRI - when different areas were stimulated, the relevant part of the brain would light up - in an amputated patient, the area of the somatosensory cortex that no longer receives sensory input no longer lights up, and another section gets larger where the sensation has been taken over
Phantom pain due to other areas taking over that part of the cortex e.g. face sensation takes over arm section and so feelings in the face also cause sensation in the arm that is no longer there as the area is being stimulated by other areas
Chemical senses - Smell and Taste (olfaction and gustation, monitor chemical content of the environment)
Adaptive roles of chemical senses - molecules of food excite both smell and taste receptors and produce an integrated sensory impression of flavour - those with no sense of smell struggle with taste
Flavour also influenced by temperature, texture, appearance of food and level of satiety
Main adaptive role of chemical senses is evaluation of potential foods in natural environments
Also have a role in regulating social interactions - pheromones are released; chemicals that influence the physiology and behaviour of cospecifics (members of same species) - humans possibly releasing sexual pheromones has received attention due to its potential, but there is little evidence to support this
Olfactory system - receptor cells located in the upper part of the nose, embedded in a mucus covered tissue called the olfactory mucosa
Dendrites located in nasal passages and their axons pass through a porous portion of the skull (cribriform plate) and enter the olfactory bulbs where they synapse on neurons that project via the olfactory tracts to the brain
Humans have 300 olfactory receptors, with each type of receptor cell contains one protein type
Olfactory receptor proteins are stimulated by the airborne chemicals and are in the membranes of the dendrites of the olfactory receptor cells
Little knowledge about organisation of system as receptors appear to be scattered - each odour is encoded by component processing (activity pattern across receptor types)
Axons of olfactory receptors terminate in discrete clusters of neurons that lie near the surface of bulbs, known as olfactory glomeruli
Each glomerulus receives input from several thousand olfactory receptor cells, all with the same receptor protein
Evidence for a systematic layout of the glomeruli sensitive to particular odours
Mirror symmetry between right and left olfactory bulbs - the glomeruli sensitie to particular odours are arrayed on the olfactory bulbs in the same way in different members of the same species
Bulbs are topographically organised and layout is random, but full arrayment principle is yet to be determined
Led to them being termed chemotopic
New olfactory cells are created throughout the individual's life to replace those that have deteriorated - they then develop axons which grow until they reach the sites of the olfactory bulb - only survive a few weeks (mechanism for locating site is a mystery)
Each olfactory bulb projects to several structures of the medial temporal lobes, including the amygdala and the piriform cortex - piriform cortex considered the primary olfactory cortex but this is arbitrary as it is the only sensory system to not pass through the thalamus
One major pathway leaving the amygdala-piriform area, which diffuses into the limbic system - mediate emotional smell response (amygdala- memory)
Another projects via the medial dorsal nuclei of the thalamus to the orbitofrontal cortex - inferior surface of the frontal lobes next to the orbits (eye sockets) - thalamic-obrbitofrontal pathway mediates conscious perception of odours
Gustatory system - taste receptor cells found on the tongue (taste buds are clusters found here) and throughout the gastrointestinal tract and are located around small proturbances called papillae
Cells either detect bitter + sweet + umami (savoury), sour or salty - three types
Presynaptic cell is the receptor cell that synapses onto the neuron carrying signals away from taste buds
Communication among other cells from the taste bud occurs across gap junctions
Only survive a few weeks before being replaced by new cells - tastes studied the most are sweet, sour, bitter, salty and umami but case has been made for others
Taste transduction for sweet, umami and bitter is mediated by metabotropic receptors
2 for sweet, one for umami and 25 for bitter
For salty and sour, mediated by ionotropic receptors - sour is transduced by 3, salty mediated by 2, one type of receptor protein per each receptor cell
Gustatory afferents leave the mouth as part of the facial, glossopharyngeal and vagus cranial nerves, which carry information from the front of the tongue, the back of the tongue and the back of the oral cavity respectively
All terminate in the solitary nucleus of the medulla, where they synapse neurons projecting to the ventral posterior nucleus of the thalamus
Gustatory axons of the ventral posterior nucleus project onto the primary gustatory cortex, in the insula, an area hidden by the lateral fissure
A different area of the primary gustatory cortex represents each taste - second gustatory cortex is the orbitofrontal cortex - ipsilateral projections
Chemotopoical organisation - each primary taste produces activity in a different area of the primary gustatory cortex
Brain damage and the chemical senses - anosmia (inability of smell)
Commonly caused by a blow to the head that displaces the brain within the skull and shears the olfactory nerves where they pass through the cribriform plate
Other less severe losses are linked to neurological disorders such as Alzheimer's, Down Syndrome, epilepsy, MS, Korsakoff's and Parkinson's
Ageusia - inability to taste
Rare, as sensory signals are carried by three different pathways
However, partial ageusia, limited to anterior two thirds of the tongue on one side, is sometimes observed after damage to the ear on the same side of the body
This is due to the branch of the facial nerve that carries gustatory information from the anterior two thirds of the tongue passes through the middle ear
Perception and attention
Prior knowledge has a major influence on how we perceive the world and our knowledge about the identity of objects also impacts perception
Knowledge about the temporal nature of sensory events also affects our perception
We create mental models of the world based on predictable and recurring sensory events - construct models of ourselves and our world via the 5 senses and this is based on prior experience
It appears that our ongoing perceptual decision making consumes a large proportion of the energy used in our brains
Even in the absence of sensory input, we still perceive - illustrated by phantom percepts; products of perception when there is an absence of sensory input - an example of this is phantom limb syndrome
Deprivation of visual input - such as glaucoma, irreversible damage to optic nerve - with some of these individuals experiencing rich and complex hallucinations
Charles Bonnet Syndrome - dependent on person's experience
Perceptual decision making appears to be mediated by several brain areas, such as the dorsolateral prefrontal cortex and posterior parietal cortex
Both structures are also involved in action decision making / imitation of physical movement
The Binding problem:
Sensory systems are characterized by a division of labour - multiple specialised areas at multople areas, interconnected by multiple parallel pathways
However, complex stimuli are normally perceived as integrated wholes, not as combinations of independent attributes
The question over how the brain combines individual sensory attributes to produce integrated perceptions is known as the binding problem
Possible solution - single area of the cortex at the top of the sensory hierarchy that receives signals from all other areas of the various sensory systems and puts them together to form percept
Claustrum - a structure made of a fine sheet of neurons located just underneath the cortex in the middle of the brain
Another solution - perception is the result of multiple interactions at each of the cortical levels of the hierarchy and this is informed by the study of communication between sensory areas in the cortex
Binding could also emerge from the constant exchange of information between many sensory cortices and within and across sensory modalities - role of subcortical structures also important
Characteristics of selective attention
Selective attention - improves perception of stimuli in its focus and interferes with the perception of stimuli not in its focus
Attention can be focused through cognitive processes, endogenous attention, or by external events, exogenous attention
Endogenous attention is thought to be mediated by top-down (high to low neural mechanisms) whereas exogneous attention is thought to be mediated by bottom up (low to high neural mechanisms)
Eye movement has an important role, but visual attention can be shifted without shifting the direction of visual focus
Cocktail of part phenomenon - focusing so intently on one conversation that you are unaware of other conversations, but the mention of your name in one of these conversation will immediately gain access to your consciousness - brain blocks all conscious awareness of stimuli except those of a particular kind while still unconsciously monitoring the blocked out stimuli just in case something that requires attention emerges
Change blindness - if we are shown, the same image with one gross feature different appearing and disappearing, we do not notice immediately that the image has done so as it seems the same; take a minute to notice the changed feature - no memory for parts of the scene that are not the focus of our attention and so we are unaware of change
Only occurs within a brief interval - without the intervals, no memory is required and the changes are immediately perceived
Neural mechanisms of attention - prefrontal and posterior parietal cortex have a role in directing top-down attention
Attention to colour and shapes for example produces increased activity in areas of the ventral stream, and attention to movement produces increased activity in an area of the dorsal stream (Corbetta et al, 1990)
Attention to identity increases activity in the ventral stream, and attention to position activates the dorsal stream (Ungerleider and Haxby, 1994)
Selective attention works by strengthening the neural responses to attended to stimuli and be weakening the responses to others - push-pull mechanism
Neural plasticity of attention mechanisms - location change of receptive fields of visual neurons, shifted by spatial attention
Covert attention is the process of attending to a sensory stimulus without fixing one's gaze - attentional gaze (shifting attention from one perceptual object to another) without worrying about confounding effects of eye movements
Studies have identities that attentional gaze neural mechanisms involve a frontal eye field which is active during attentional gaze
Stimulation of neurons here at intensities lower than the threshold for eye movements, leads to improvements in the detection of stimuli through covert attention - frontal eye field mediates shifts in visual attention, though other brain areas are also implicated
Also selective attention to auditory, gustatory and olfactory stimuli, not just stimuli
Simultanagnosia -
visual simultanagnosia - difficulty in attending visually to more than one object at a time, because the dorsal stream, including the posterior parietal attention cortex, is responsible for visually localising objects in space and has become damaged
Also associated with bilateral damage to the posterior parietal cortex, in which stimuli are identified as though they are presented individually, even when they are not
