attention and consciousness

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  • Created by: Kelseyb
  • Created on: 08-01-18 21:17

differences between certain 'awake' states

  • Covert attention = direct our mind to the attended object 
  • Overt attention= direct most sensitive part of our sense organs to attended object (fovea of the eye)
  • Voluntary/endogenous/top-down/sustained= attend through willful act, process that environment more efficiently. usually provoked in lab by presenting an attentional cue which subject can decode + direct attention to cued location. have control over allocation of attention (certain feature, location, object)
  • involuntary/exogenous/bottom-up/transient= unexpected, automatic attention. no control over allocation of attention. improves stimulus detection at attended location for short period of time (200-250ms) but has deterimental effect that lasts 600ms. after external event or object has captured attention. = inhibition of return. 
  • Top down and bottom up differ with respect to areas that generate the attentional signals + regarding their influence on stimulus detection. 
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electrophysiological signatutres of top-down atten

  • employing covert attention task= larger P1 component when subjects attended to contralateral visual field 
  • top down attention tasks = advantage that participants either attend to: specific location (spatial attention), specific feature (feature based attention), or specific objects (object based attention)
  • Feature and object based attention do not result in the difference of the P1 component while latter components of ERP are affected
  • Effect of attention occurs later in visual cortex (70-100ms) than auditory cortex (20-50ms)
  • .visual repsonds with longer latency compared to auditory. not that early selection occyrs in auditory and vice versa. 
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Attention and visual search

  • to find relevant items- direct attention to specific features + ignore others
  • visual search= distincitve feature pops out (e.g. colour) 
  • pop out search= time it takes to find object depends on whether or not an item pops out. under conditions item carries distinct feature that can be processed pre attemtively (red T amongst green Ls)
  •  if item has no distinct features= search time dependent on number of items in display. 
  • conjunction search= neccessary to search for presence of multiple features in an item (look for red circle embedded in in red and green crossesand green circles)
  • conjunction search- have to move spotlight of atnetion to more locations if more distractors present- takes more time. - feature selective attention to guide spatial attention. explains increased search duration. 
  • search time depends on number of distractor items that share relevant features. 
  • tested covertly, conjunction search. search then distinguished. visual probes present at locatations that previously been occupied by feature
  • P1 component larger when probe was flashed in contralateral visual  field that previously contained item with relevant feature 
  • visual search seems tp automatically label the potentially relevant items and process those locations more effieicentl- neurophysiiological correlate of feature selective attention
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attentional modulation

  • Tootel et al 1998- attention modulate activity in early visual cortex + higher visual cortical areas, modulation stronger in higher cortical areas. 
  • spatial top down attention alters the firing rate of neurons in cortical areas= V1, V2, V4. 
  • Moran and Desimone (1985)- attention to one of two stimuli strongly modulated the response of the recorded neurons. 
  • later studies provided unambiguous support for modulation of spiking responses in early visual cortex too (Motter 1993)
  • Reynolds et al 1999.- measured response of neurons in V4 to different stimuli presented inside the receptive field. as most neurons are selective for certain features, some stimuli elicited strong responses and others weak. 
  • if two stimuli presented simultaneously in receptive field, response was average of two responses even though each individually activated the cell. 
  • less effective stimulus reduced the cells response to the more effective stimulus even though it excited the cell when presented alone. 
  • suggests stimul in visual world 'comepte' for prrocessing resources. 
  • attention eliminated the mutual influence. when attention directed to weak stimulus, cell responded asif only weak stimulus present and vice versa. competion biased in favour of attended stimuli because of bias receives from attentional system (biased competition model of attention) bias comes from higher cortical areas. 
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attentional modulation (2)

  • Human FMRI experiments to see if same effect
  • fmri bold responses measured in V1 and visual areas (V2,V4, VP TEO) when one of 4 consecutively presented single stimuli were present in upper right hemifield, and when all 4 presented simultaneously. 
  • simulataenous- resulted in reduced BOLD singnal in V4 and TEO, which suggests competition between simultaenously presented stimuli 
  • when attention now deployed to one of the 4 stimulus locations, the BOLD signal in v4 and TEO same for consecutive and simultaenous stimulus competition. 
  • asif the attention filtered out the irrelvant distraters. 

is activity at level of lateral geniculate nucleus already modulated? (even earlier stage)

  • subjects asked to attend to one or the other visual hemifield while checkboard flashed in both
  • BOLD signal recorded in the LGN and in v1 representing attended visual field larger than in BOLD representing non-attended hemifield 
  • attention modulates processing at very early stage (O'connor et  al.2002)
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Feature based attention

  • feature and object related attention do not show different P1  ERP components while later ERP components were affected.
  • different areas of visual system process different types of information. segregation fairly pronounced
  • in the primate almost all iformation has to pass through area V1. from  here information is distibuted to different secondary visual areas of temporal and parietal cortex. 
  • given different areas process different types of visual information, they will be differently sensitive to certain features of a stimulus. e.g. whether a stimulus moves or the colour. 
  • area V5/MT particularly sensitive to moving sitmuli + involved in motion processing and signalling
  • area V4- colour and shape processing and signalling. 
  • would expect area more sensitive- more active when that feature is attended to 
  • initial PET studies show attention to specific features activated non-overlapping areas of the visual system (studies no spatial resolution to assign the activity differences to specific areas)
  • recent FMRI studies- combined retinotopic mapping with features attentive studies + follow up MEG measurements. 
  • subjects asked to attend to 1)direction of motion or 2)colour colour of stimulus and report the feature value
  • attend to colourV4 increased. motion MT increased.  differences as early as 100ms after stimulus 
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Object based attention

  • location and certain features of an object - low processes.
  • retinotpic maps- location based. 
  • features represented in feature map. 
  • both only part of object representations.
  • if attention directed at objects aswell- effects should be present in higher order area where entire objects represented not just the features
  • if object based attention exists then- cuing one part of object should affect our reaction time to events happening at different parts of object as attention should already be present in these parts
  • Egly (1994)- FMRI- object based attentional signals present in early and intermediate visual cortex. design mixes spatial and object based attention.
  • O'Craven 1999- didnt mix. faces and houses seemed to be represented in seperate parts of brain. 
  • fusiform face area= sensitive to presentatio of faces
  • parahippocampal place area- sensitive to presentation of houses and places
  • superimposed house and facial stimuli so both were visible
  • one of them moved whilst other stationary
  • attend to either 1)face 2)house 3)motion
  • each activated specific areas- attention to objects exsts indep. of spatial attention. selectively increases activity in area specialised/
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attentional networks

  • Source areas of attention= executive control systems of the brain control where and what we attend to.  attentional signals arise in this area.
  • Site areas of attention= areas affecred by the control signals (sensory areas). attentional signal influence sensory processing within these areas. 
  • certain lesions result in attentional deficits and these were not usually located in sensory areas but areas of : Parietal cortex, Frontal cortex, pulvinar (part of thalamus), or the midbrain (superior colliculus)
  • Feedback connections from source areas influence the processing in site areas. 
  • Hopfinger et al 2000: cued subjects attend 1)right 2)left of the visual display, 8s after cueing no stimulus appeared. imaging data over these 8 seconds determine which part of cortex are active in guiding attention as would not be contaminated by activty related to stimulus presentation. found: superior frontal cortex, inferior parietal cortex, superior temporal cortex, parts of cingulate and insular cortex active after cue presentation (providec cue directed subjects attention)
  • on control when cue presented and subject required to keep fixating, none of the above altered activity on trials. 
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bottom up attentional networks

  • Bottom-up= not same. allocating attention to a location where an unexpected stimulus appeared involves a part of the parietal cortex called the temporo=parietal-junction, part of the temporal cortex called the middle temporal gyrus and parts of frontal cortex called middle frontal gyrus and inferior frontal gyrus. 
  • corbetta et al.2000-  valid-invalid cuing paradign, presentation of a target at a non cued location (invalid) resulted in activation of the above areas. 
  • activity predominently in rufgt hemisphere. 
  • areas not active if target appears in the same locations when location has been cued (valid)- not induced by stimulus
  • mental operations neccessary for stimulus detection when unexpected- cue will have resulted in attention being deployed to a certain location. the stimulus is localised (to report it in an unattended location) and attention needs to disengage from the current location, move to the stimulus location. engage there and inhibit other locations. 
  • the network may be particularly involved in the process of disengagement and re=orientating.

two forms of attention that exist- different biological basis, controlled by different corticol networks. 

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Premotor theory of attention

  • Rizzolatti et al 1987
  • top-down attention
  • motor/premotor planning- particular rapid eye movements (saccades)
  • if we attend covertly to location, we are planning a saccade to that location
  • if we fixate the stimulus of interest, we can analyse it with the best resolution
  • during covert, we simply do not execute the planned sacade
  • undisputed certain areas that are important for execution of saccade eye movements are also active during covert attention
  • parts of parietal cortex, frontal cortex, superior colliculus in midbrain 
  • neuorns in these structures fire more strongly to stimuli placed in their receptive field when animals planning to make saccade movemement to that location in near future, compared to when fixate passively or plan eye movement elsewhere, 
  • if recording sites stimulated with small electrical pulses, activaing neurons at those sites, animal will make a saccadic eyemovement toward the location the nerons represent in terms of visual space
  • certain min amount of electrical stimulation required to elicit a saccade
  • small electrical pulse= some neurons at stimulation site will still get excited but not sufficient to trigger eye movement 
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Premotor theory of attention (2)

  • since some neurons are still excited, does that mean that attention is still allocated to the location these neurons reprsent, even if no saccade is triggered?
  • Moore & Fallah 2001- probed wether electric microstimulation in FEF increased an animals abilit to detect targets in noisy environments. effects specific for targets presented at sites the neurons represented, targets placed slightly away from these spatial locations not detected more easily. 
  • Moore & Armstrong 2003- electrical microstimulated FEF neurons and simultaneously recorded in visual areas V4 . ensured receptive fields of V4 neuron overlapped with location FEF encode for
  • hypoth- feedback connections from 'higher' area FEF would gate flow of info in sensory areas, such that stimulus presented in receptive field would elicit stronger response
  • argument is that microstimulating FEF is uequivelant to attention being deployed to the location FEF neurons represent
  • attention enhances stimulus driven firing rates in SITE areas (+ thus increases BOLD signals if FMRI measurements obtained)
  • stimulus driven resppnses in V4 increased- if FEF and V4 didnt overlap-  no effect
  • direct evidence feedback signals from higher corticial areas are instrumental in gating stimulus driven reponses + thus increase saliency of those stimulu, improving perceptual abilities
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neglect and extinction

  • unilateral lesions to parietal cortex (stroke) - unilateral spatial negelct and extinction. 
  • neglect- ignore the side contralateral to the lesion 
  • extinction- difficulty perceiving objects in the hemifield contralateral to lesion 
  • neglect occurs much more for stroke to right than to left parietal cortex - unique to humans
  • representational model- right hem represents space and attention for both hems. left only has a representation of right hemispace and attention
  • if right hem is lesioned- left hem not represented anymore
  • Attentional bias model- left hem stronger bias toward contraleteral side than the right. in healthy subjects- overcome by mutual inhibition between the hemispheres. if right is lesioned- mutual inhibition gone + bias toward right is obvious
  • valid-invalid cueing paradigm- patients with mild neglect. showed mostly deficit if a stimulus appeared in the contralessional side when it had not been cued. (invalid trial). from RT was infered that extinction like results due to deficit of disengaging attention from ipsiesional side. 
  • some found- inferior parietal lobule and temporparietal junction are areas of substantial lesion overlap. 
  • more recent study- areas of overlap mostly within superior temporal gyrus, insula cortex and basal ganglia. 
  •  
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neglect and extinction (2)

  • 2 prominent neglects:
  • Spatial neglect= neglecting space contralateral to lesion
  • object based neglect= neglecting side of an object that is contralateral to lesion but which may be in ipsilateral space relative to lesion
  • spatial neglect usually associated with lesions in parietal cortex (inferior parietal lobule, temporoparietal junction) 
  • object based neglect- lesions in temporal cortex (superior temporal gyrus)
  • neglect also affects memory systems (not just analysis of sensory information)
  • subjects with spatial neglect ingnore side contralateral to lesion if asked to image a well known visual environment 
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