PY2507.6 ~ {Neglect}
spatial attention
brain's ability to selectively focus on a particular location in space and process info from that area more effectively than unattended regions
spatial-attention deficits
simultanagnosia + neglect [spatial cog is not limited to vision only]
what is neglect (Halligan & Marshall, 1991)
cog inability to respond to objects and people located on the side contralateral to a cerebral lesions
what do people with neglect typicalaly do
they orient their gaze to the right and ignore what happens on the left side [so anything on that side they don't pay attention to]
causes of neglect
unilateral brain damage [esp in RH] leads to failure to attend to contralesional side of space [left] damage can involve cortical [most common], subcortical or white matter regions
why RH lesions cause more severe neglect
RH attends to both sides of space, whereas the LH primarily attnds to the right side only [so lesion on the right results in left neglect cause LH can't compensate]
neglect symptoms
ipsilateral bias in - spontaneous behaviour [orienting towards ipsilesional side and neglect of contralesional] - in navigation, grooming, shaving, eating food etc + test-elicited behaviour [in visual/motor tasks]
somatoparaphrenia
symptom associated with neglect - denial of ownership of limbs on left side of body, patient fails to recognize that the left arm/leg belong to him
symptoms associated with neglect but are different
hemianopia - primary visual field deficit - loss of half the visual field in both eyes
hemiplegia - primary motor deficit -paralysis or severe weakness on one side of body
which pen and pencil tasks can be used to demonstrate neglect
line cancellation [patient cancels on right side only] + line bisection [representation of middle is towards to right] + shape cancellation
spontaneous visual search Karnath & Dieterich, 2006
neglect [patients show an ipsilesional bias in eye movement patterns] so to the right typically
2 key distinctions used to classify varieties of neglect
double dissociations in neglect + observer/enviro centered [egocentric] vs obj/stimulus centered [allocentric]neglect
double dissociations in neglect
kind of evidence in brain science that shows 2 cog functions are controlled by separate brain systems space vs objects
perceptual vs motor tasks
near vs far space
enviro-based [space-based neglect] & object/stimulus-based neglect
enviro - patient ignores contralesional side of space [left is left in eniro regardless of what object is there [viewer centered]
obj - patient neglects left side of individual obj no matter where they are in space
perceptual vs motor neglect
p - inability to attend to or perceive stimuli in contralesional space [even though their sensory systems are intact]
m - failure to initiate or direct movements toward contralesional side [even though patient can perceive stimuli there]
Curved hand paths in neglect (Goodale et al, 1990).
neglect patients show ipsilesional bias in reaching paths - provides evidence that neglect can affect not only visual perception of space but also motor planning and execution
neglect for near vs far space Guariglia & Antonucci (1992); Berti & Frassinetti (2000)
results showed that some neglect patients have difficulties specifically with near space neglect so patients were better at detecting obj in far space [outside arm's reach]
what causes ipsilesional bias
sensory theories predominant: neglect is caused by failures of sensory processing [on contralateral side] occurs because sensory input from neglected side is not processed as efficienlty so patients don't attend to it
what does the variety in neglect mean for deciphering what causes it
no 2 patients are identical in their presentation of neglect so a single theory cannot account for all cases
Milan square study Bisiach & Luzatti (1978)
patients described the sqaure from imagination and neglected the buildings to their left even when changing vantage point [deficit in representing space even when it is imagined]
representational deficit in Neglect
space is topographically represented across the 2 hemispheres so damage to one destroys the representational analogue of the contralesional real world
extinction
presenting stimuli on right impairs processing on the left so the presence of the ipsilesional stimulus prevents awareness of contralateral [when they are put together]
extinction redcued by grouping
the task would be to press the bar when you see 2 squares so when theres more shapes its easier than when theres less -ipsilesional side outcompetes contalesional for attentional resources - low-level visual grouping between items can reduce extinction [processed as one object and grouping reduces their competition]
visual detection studies (Posner et al., 1982) - neglect can be manipulated through cueing
patients fail: to detect stimuli on left when an invalid cue is presented on right + when interval between cue and target is short [less time to switch attention] BUT cueing position on left produces almost normal perfomance
interpretations of visual detection findings
patients with neglect have difficulty disenganging attention from ipsilesional side and redirecting to contralesional + right side has a magnetic effect on attention making it difficult to focus on left
bottom-up attention [stimuli drivem]
stimuli themsleves help grab attention even when patient is typically negleccting that side - Humphreys & Riddoch (1993) suggests that salient stimuli [those that stand out] can force attention to neglected area
top-down attention [goal driven]
patient voluntarily chooses to focus on neglected side due to external incentives or goals - Russel et al. (2013) shows perfomance in detecting items on left is improved when given an incentive
priming and decision making
patients may fail to recognize obj on neglected side verbally but show signs that they're processing info unconsciously - (Ladavas et al., 1993; Della Sala et al., 2013) point to the house you'd ike to live in
Kinsbourne - orientational bias
each H drives att in a way that forms an attentional grad along a continuum [the closer a stimulus is to H's controlled side stronger attention to it becomes] - each H tends to pull att towards contralateral space but there's a bias in favour of right
Heilman - attention/intention
proposed that neglect happpens due to prob with attending to left side or intending to act toward left side [due to damage in the right side] so not visual issue but att + action planning one caused by imbalance between H
rehabilitation techniques for neglect
rehab focuses on activating neglected side using diff brain systems = combining perceptual & somatosensory att [activating attention to neglected side] + use of motor tasks [reaching is better than pointing]
lateralized arousal
stimulating one side of body to boost att to that side = caloric. vestibular stimulation [putting cold water into one ear canal which stimulates vs tied to spatial awarened] - results in temporary improvement + vibration of left neck muscles = stimulates proprioreceptive input on neglected side
non-lateralized arousal
increasing overall alertness or motivation without focusing on one side of space - giving rewards for attending to left side + makiing tasks more excting / engaging + playing motivational music - offering feedback