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Flashcards in Spatial attention Deck (19)

What is spatial attention?

Attentional processes that select visual stimuli based on their spatial location // involves directing attention to a location in space. It can be voluntarily altered; loss of clarity the bigger the region is.
- Protects us from sensory overload

Likened to: Gaussian gradient (Downing and Pinker 1985) & zoom lens (Eriksen et al. 1990)


Hemispatial neglect

**Failure to direct attention to one side of space; person behaves as if information in the world on the side opposite to the lesion does not exist

- can be all senses
- heterogeneous collection of SYMPTOMS (why its hard to define precise neuroanatomical correlates) --> component deficits. BUT key one = no attention to one side of space
- frontal + parietal region involved in spatial functions (i.e. deployment of attention) are also involved in non spatial processes such as ability to maintain performance over time - will exascerbate key features of neglect ALSO neglect symptoms can fluctuate (Li & Malhotra, 2015)

Parton (2004)
some say:
a) core = neglect comes from an impaired representation of space
b) others = reflects a directional motor impairment (cant initiate or program contralesional eye movements)
**these can obvs co occur in same patient

** logic and knowledge can have an impact; for example with clock drawings, they know that there should be 12 numbers so they include 12 but spatially wrong
- Extinction = less severe form of neglect (ignore contra side when ipislat presented)


Neglect & the dorsal stream
- prefrontal cortex

- allows for selective attention shifts (controlled shifts of attention) (Mirsky, 1989) in in tact subjects
- problems aren't as common as w parietal lesions (Bisiach and Valar, 1988)


Parietal lobe & neglect

- normally comes from patients with middle cerebral artery damage (stroke)

all this = Dorsal stream: V1 &V2 --> Posterior/inferior parietal --> frontal ((Milner & Goodale, 1995)

- Intraparietal sulcus has a role in this attention & TPJ (Vandenberghea et al. 2012)

c) dorsal and ventral do interact (Van Polanen & Davare, 2015) = E.G. ventral important for controlling complex object-oriented hand movements

**strokes to posterior c artery = might affect occipital lobe = hemianopia. NOT same as neglect (Mort et al. 2003)


Other neurological disorders related to the dorsal stream:

- optic ataxia - difficulty reaching visual goals
- akinetopisa - motion blindness
- apraxia - individual has difficulty with the motor planning to perform tasks or movements when asked


What is neglect NOT a problem with?
- how can we see the symptomatology of neglect?
- These had dorsal stream damage

**figure-ground segmentation**

1) Driver, Baylis & Rafal (1992): patient C.C with dorsal stream lesions
a) yellow box/blue box thing
- left leglect occured when the box was on the right (cos left of the object) = object segmentation FIRST
- Neglect occurs @ later stage of processing (there's a preattentive segregation stage then an attentional stage)

assumes that they see this as yellow on blue background? They do cos:
- Lamme (1995) = brighter colour texture makes it stand out as figure

i.e. this shows that neglect occurs later on in the process on individual figures BUT this doesn’t show that segmentation processes of totally normal…

2) Driver et al. ^ conducted another study using visual symmetry (symmetry around the vertical influences figure-ground segmentation). The premise:
a) When other factors are equal, symmetrical regions tend to be seen as figures against asymmetrical backgrounds by normals

"just tell us which shapes are red or green"

- reported the colour of the symmetrical shapes (i.e. detected figure from ground)
- BUT couldn't report that they were symmetrical (neglected one side)
- Symmetry judgement require later stage of attentive processing

3) SAME for patient R.B (1994)
- He reliably picked symmetrical shapes as figures rather than the intermingled asymmetrical shapes
- Couldn't draw one side of the shape

4) Mattingley, Davis & Driver (1997): dorsal stream damage
a) Box and bar: when the bar was perceived to go through the box = no prob. BUT when "split up" was a prob
--- gestalt law of good continuation (?) - perceive as whole object -- attention is on whole object (no segregation)
** Object perception can operate prior to selection by parietal cortex**
makes sense: parietal is downstream i.e. goes to occiptial first then to parietal (more complex)



Motor control and parietal damage

Tegne´r (1991) - shows a motor deficit in neglect. BUT Used patients with large lesions to the frontal lobe & tasks which required them to make unnatural arm movements and move away from the targets in line cancellation.
Frontal lobe lesions may perform abnormally b/c of difficulties with highly incompatible responses (Mattingley, J. B. & Driver, 1997)

Mattingley et al. (1998)
- Looked at IPL and IFL focal lesions separately & doesn't require patients to move away from target
- direction of movement manipulated (i.e. start pos of hand)
- with left neglect & hand in the middle = much slower to press target on left
- with left neglect & hand to the left of target = no impairment in moving hand to right


case studies - evidence for a bit of a distinction of ventral and dorsal (2)
(Example of dorsal damage)

1. Patient DF:
a. visual agnosia + damage to temporal lobe
b. object perception effected. But Grasping movements not different from controls

2. Patient RV with bilateral parietal damage (Goodale & Milner, 2004) --- CAN COPY drawings but can't grip things
a. optic ataxia + bilateral parietal lobe damage
B. can copy drawings but cant grip things

spatial attention needed for successful hand gripping (Garaza, 2013)


the "when" pathway

- parietal damage patients aren't helped by preview searches (temporal aspect involved). Non parietal damage are fine with it; it improves their performance (we mark things that we have already/attended to) (Olivers & Humphreys (2004)
MT --> TPJ (predominantly right) (Batelli et al. 2007)


Evidence for right parietal involvement in temporal processing (4)

1) Rorden et al. (1997)
- TOJ bar task & parietal ppts
- Tend to perceive the ipsilateral stimulus as coming first
- Need affected side of space (in neglect) a big head start for them to notice that it came first = they also have a temporal problem

2) Woo et al. (2009)
- TMS on healthy normals
- TMS to right posterior parietal cortex (not left) = delay in in contralateral processing in a TOJ task

3) Roberts et al. (2012)
- Lesion study
- most studies have looked @ TOJ and spatial aspects
- spatial + temporal aspects were correlated: worse temporal resolution being associated with increased spatial biases
- TEMPORAL DEFICITS = right temporoparietal regions
- cerebellum = plays a role in timings (Aso et al. 2010)

- Motion perception = spatial and temporal properties
- right IPL is significantly active while subjects perceive a stimulus moving in apparent motion (Batelli et al. 2007)
- EEG showed a correlation between EEG signal in the right parietal lobe and the illusory perception of a rotating wheel that required discrete motion processing Van Rullen et al. (2007)


Why does temporal aspects = neglect?

Becchio & Bertone, 2006
- the damaged parietal lobe = damaged sense of
- italian plaza experiment
- falls from the patients representation BUT ALSO from their conception
- the permanence of the objects (inc their future/past) is impaired
- dissocation in TIME


TOJ evaluations

- Stigchel + Nijboer (2013) -- validated measure

- Response bias (Shore et al. 2001) neglect ppts are more likely to report that their ipislateral side came first

- stimulus characteristic variation creates a lot of variation in the literature (i.e. band clicks vs tones) (Fostick, Ram-Tsur, Babkoff, 2011)

- different modalities will affect the perceotion of temporal order (i.e. auditory and visual) (King, 2005)

- can pick up on spatial and temporal deficits in dyslexia (Liddle et al. 2009) (avoid phonemes)


Line bisection task - Who + what? + Characteristics

Schkenberg, Bradford and Ajax, 1980)
- the score is the length by which the patients estimated centre deviates from the actual centre
- evaluation relies on judgement and common sense
- length of line affects the result --> SHORTER LINES people are less likely to deviate from centre
- Right lesion move line to right & left lesion move line to left
- more sensitive for RH lesions


Evaluation of Line bisection task specifically

karnath and Ferber (2001)
- report that 60% of their well-doc’d inattention patients were identified by line bisection techs

1) older subjects are worse @ this vs younger subjects in non-damaged ppts + males make slightly larger leftward errors than do female subjects.


Cancellation tasks EG and FOR

- E.G. star cancellation task (Halligan et al. 1991)
untimed// detect all the small stars

- dense cancellation tasks with distractors are usually better and more sensitive in detecting neglect than the simpler cancellation tasks that have no distractor items (see also Halligan et al. 1991)

- cheap & easy
- designed to increase task sensitivity to inattention by increasing its difficulty
- Identified all of 30 ppts (26 right and 4 left) inattention (Halligan et al. 1989)
- more sensitive than line cancellation

b) cancellation tasks detect neglect more frequently than any other single test, although there are a few patients who perform well on cancellation but show neglect on other tasks—hence the need to use more than one screening measure for neglect (Halligan et al. 1992


Line bisection tasks & cancellation tasks AGAINST (7)

- not very well standardised

- the patient may have extinction; many patients with neglect show extinction - may be a part of the syndrome? NO cos its not present in all neglect patients. Extinction may also be cross modal (EG visual stimulus to the right “extinguishes” a tactile stimulus on the left) (Driver, 1998)
- extinction is associated with damage to the right TPJ Meister et al. (2006)

2) These tests are often used as a binary classifier to simply identify the presence or absence of spatial neglect, even though it is clear that there is a spectrum of disability on these tasks:
a) Center of Cancellation (CoC) task was invented to assess the severity of the neglect

3) Hemianopia: Parton et al. (2004) QUITE common to occur together; hard to separate the two.
a) hemianopia + no neglect were biased on the same side as their hemianopia... attempt to compensate for it?
BUT This bias was less than the ipsilateral bias of patients with hemineglect.

4) A primary lesion restricted to the visual cortex does not necessarily produce lateralised inattention but still may result in line bisection error (Bainer et al. 2010)

5) Cant decipher the different neglects (Halligan, 2003)
- may have motor neglect & can only use one side of their body but be able to perform fine on this task// personal neglect (ignore one side of face w make up EG)
**should make them do the task with both hands
6) Norton et al. 2016) parkinsons patients who have be tested for neglect but have motor deficits

7) Task fatigue makes inattention more likely: Fleet and Heilman (1986) recommended that tasks like letter cancellation tests be given in a long series to improve the likelihood of eliciting evidence of inattention


Line bisection tasks vs cancellation tasks
which regions?

CANCELLATION TASKS: more likely decipher patients with anterior OR subcortical lesions than line bisection tasks (fronto-parietal)
BISECTION TASKS ARE MORE sensitive to the posterior lesions (parietal-occipito) (Vossel et al. 2011)

Line isnt as sensitive for neglect & ^ so must be measuring something else:
a) line = allocentric object processing
b) cancellation = egocentric processing

---> thus a careful examiner will not rely on one test of inattention if the behaviour/site of lesion suggests an inattention problem


Clock/ copying tasks

- easy test for neglect // screening test for neglect @ bedside
- these are not very sensitive on their own and are also not always easy to score in a graded manner (Azouvi et al. 2002)
- constructional apraxia may perform poorly on such task even tho they show no spatial neglect


battery of neglect

Behavioural inattention test (BIT)
- - no single test alone is able to detect neglect in all patients (Azouvi et al. 1996)
Moreover, there are many reports of clear dissociations, with some patients showing neglect on certain tasks but not on others. (Ferber, 2001)

made up of behavioural tests
(menu reading/map reading) & conventional tests (line crossing/ star cancellation etc)
******provides info on how everyday behaviours are affected and also of the visual attention phenomena