chapter 4 Flashcards
Synaesthesia
condition in which sensory input of one modality is consistently and automatically experience as a sensory event in a different modality (e. g. seeing color on hearing musical notes)
- also within the same modality ( seeing a letter, seeing a color)
- Most common: experiencing color on seeing or hearing a letter, number or word.
- Usually unidirected
- only Low-level percepts like colors or special location
- genetically or environmentally
- Almost all report having the condition as long as they can remember
- appr. equally distributed in men and women
- automatic and mandatory
two kinds of synaesthetes by Dixon
Projectors: experiencing the colour as if it is in the physical world
Associatiors: see the color in their ‘mind’s eye’ (90 %)
Synaesthestes and the Stroop test
-if the inducer colours are congruent with the synaesthetic colours, they are faster
- if incongruent with the synaesthetic colours, they are slower
= synaesthesia is mandatory and automatic
- participants were better in answering questions in the colour of the answer (7 is green, question was 3 + 4 in green) than if not, therefore the effect holds even if the colour is not present
Mattingley (2001)
tested synaesthetes with visual masking tasks in which they were primed without conscious awareness
=> found that conscious awareness is necessary for synaesthetic responses
-> synaesthete’s interpretation is crucial rather than the physical properties of the stimulus, which predicted the synaesthesia.
visual search paradigms (Edquist et al., 2006))
Since letters are experienced as being colored tests were made if they are better in detecting letters between other distractor letters, as would the FIT theory suggest => No they aren’t: no built-in advantage in separating it out from blue distractors
-> Another proof that conscious awareness is necessary
fMRI, EEG, & TMS studies on synesthestes
- results suggest that there is activation in related regions (colour for people seeing numbers), but all this measurement instruments are unprecise
- signal for word-colour form in the area V4 for colors was found (not measured in normal people) BUT other studies failed to detect this activation
- activation in frontal & parietal lobes, particularly in the intra-parietal sulcus (IPS) = IPS integrates sensory information from different modalities
fMRI, EEG, & TMS studies on synesthestes
- results suggest that there is activation in related regions (colour for people seeing numbers), but all this measurement instruments are unprecise
- signal for word-colour form in the area V4 for colors was found (not measured in normal people) BUT other studies failed to detect this activation
- activation in frontal & parietal lobes, particularly in the intra-parietal sulcus (IPS) = IPS integrates sensory information from different modalities
brain functions in synesthestes
- Brain always integrates information across modalities to develop a useful model of the world
In synaesthesia: regions related to the perception of the inducer become linked to regions related to the experience that the former activates the latter
-> Available in everyone, just stronger in synaesthetes or inhibited in non-synaesthetes
Theory suggest that we all had the connections as strong, but they are usually pruned out in early childhood
‘Dishinhibited-feedback’ theory
-> connections are there in everyone , but the activity is usually inhibited
- LSD and other hallucinogenic drugs can induce temporary synaesthetic experiences
-> LSD involves the disinhibition of existing pathways
Functional imaging evidence supports this theory
Synasthesia conclusion
- some people with synesthesia have enhanced memory and mathematical manipulations and many synaesthetes are drawn towards creative arts
- Synasthesia can take on many forms
- it runs in families
- it is automatic & mandatory
- it requires conscious awareness
- it can be seen as evolutionary disadvantage
Blindsight
- restricted visual field due to brain damage
- Scotoma = A blind area within the visual field, resulting from damage to the visual system
- Damage to left striate cortex will result in blindness in the right visual field of both eyes and visa verse
- People were able to point to a light source on their ‘blind sight’
The patient DB
- was able to report details about objects appearing in the blind areas, but no conscious experience of seeing them:
- Detect presence
- Indicate location in space by pointing
- Discriminate between moving and stationary
- Between horizontal and vertical lines
- Distinguish letters X and O (unable to distinguish X and triangle and other letter => X and O dependent on low-level characteristic of these stimuli)
- Was not able to distinguish between rectangles of various sizes, between straight- or curved-sided triangles
- -> people do perceive something but without being conscious aware
sceptics to explain blingsight
- Blindsighted patients might responding to light, which was reflected from the object onto functioning areas of the visual field (stray light)
- > BUT this fails to explain how DB distinguishes X and O
- > evidence against the stray light explanation came from DB’s inability to respond accurately to objects whose image fell onto his blindspot(= where the optic nerve passes through the retina and where we are all blind)-> we would expect him to perform equally well whether the image fell on blindspot or in the scotoma.
- -> DB could not detect objects presented at blindspot, but those presented to scotoma( immediately adjacent to the blindspot)
- Computer screens that use ‘raster displays’ give a ‘ghost’ image on the other side of the screen that can explain some blindsight patients abilities
- islands (no proof)
- Change in response criterion but not in sensitivity
- Patients equally sensitive to the presence of a stimulus but less willing to report conscious awareness
- change in response criterion but also qualitative change
islands ( Kentridge et al.)
Small areas or ‘islands’ in the scotoma within which vision is spared and blindsight might be mediated by what is left of the primary visual pathway rather than other secondary pathways.
- Kentridge et al. looked for scattered regions of spared vision in one patient using a procedure which ensured that the effects of eye movements were abolished. Under these testing conditions, they noted that blindsight did not extend across the whole of the area of the scotoma, but was evident in some areas even without eye movement,
conclusion : although there may be some spared islands within the scotoma, these cannot account for all blindsight.-> study not been evident in patients eye sight and not been proven in the MRI
two-alternative-forced-choice tas
test in which one of this two time intervals was the signal
-> showed that there is not just change in response criterion, but also by qualitative differences
widely accepted explanation for blindsight
two separate visual systems :
1. primitive non-striate system => sensitive to movement, speed, and other characteristics without conscious perception, function : localize
2. More advanced striate system => conscious perception, function: identify
=> Perhaps blindsight represents the working of the primitive visual system whose functioning is normally masked by the conscious perception
-the two system might be incompatible types of representation, therefore only one of them became access to consciousness
DB rather..
felt than saw something
-> however, blindsight is a very poor substitute for normal vision with significantly reduced sensitivity to fundamental aspects of the scene
Unilateral spatial neglect (USN)
- difficulty in noticing or acting on information from one side of space typically caused by a brain lesion to the opposite hemisphere.
- Also called hemispatial neglect or hemispatial inattention.
- Patients fail to respond to stimuli which they can see
- Main reason: Stroke)->84 % of patients with damage to the right hemisphere from stroke show symptoms
- > 64 % of patients with damage to the left
- > Right hemisphere lesions are more severe and persistant
Odd behavior of people with USN
Ignore people approaching from the damaged side, eat food only from the side of the plate they see, wash and dress only that side, draw a clock only on the right side
- Patients can remember places they were from one side and if they imagined to stay at the opposite square, they remembered the other side
- Patients would choose a not-burning house over a burning house, even if they failed to recognize the fire
-Patients with USN have difficulties remaining focussed
Difference USN & visual field loss (VFL)
USN can exert an influence across modalities: over haptic & somatosensory perception, smell, audition, imagery
VFL restricted to vision (blind area moves with the eyes)
