8 May 00
Glyn Humphreys
series of seminars marking the end of Martin Davies� tenure (Wilde Reader in Mental Philosophy)
consciousness = highest profile topic in inter-disciplinary research in cognitive science
it can mean more than one thing
mystery - the hard problem of consciousness (Chalmers)
phenomenal consciousness
access consciousness � some information is available to be used by us as agents in the rational control of speech + planning for action
action <�/span> perception loop
how you act is influenced by how you see the world as being
how you intend to act upon the world
the way you intend to act upon the world splits up in neuropsychological cases
Glyn Humphreys + M Jane Riddoch � �To see and not to see�
Martin Davies + Glyn Humphreys � �Consciousness�
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conisderable evidence from experimental psychology and neuropsychology for unconscious processing of stimuli (those which we can�t express a specific response)
e.g. blindsight
priming + preference judgements on stimuli in the neglected field
forced choice judgements in alexia (unable to explicity read the stimulus)
shows the effects of stimuli that they report not being aware
even though they may feel that they�re guessing, they�re told not to mind that � intentional behaviour corresponds to the location of the stimulus
intentionally based, even though affected by things they�re not explicitly aware of
other instances where beahviour is generated without intention
ERPs in neglect
GSR in psopagnosia (galvanic skin responses to people they know)
are unintentional actions contingent on low-level mechanisms, with simple input-output relations?
can unintentional action be found on behaviuors that are normally controlled by intention:
reaching and grasping an object
whole sequence of action
Reason (1984) � diary studies of �slips of everyday action�:
e.g. taking a new route a long a familiar path (don�t turn left at the usual junction)
where the action you�re carrying out conflicts with the higher-level goal you�re setting up
slips of action when concentrating on something else
S-R contention scheduling system modulated by supervisory attentional system (priming/inhibiting some responses, e.g. the familiar route)
intentional behaviour is determined by the Supervisory Attentional System in a unitary fashion
but here: intentional control of behaviour can be fractionated in a number of ways:
neuropsychological evidence based on slips of action. fractionation of:
control object selection
control of action selection
external and internal control mechanisms
utilisation behaviour (serious disorder, damage to frontal lobes)
grasp reaction to stimulus, even though told to do something else and not touch the stimulus (put the glasses on instead of putting on the table, with more and more glasses)
utilisation behaviour = extreme example of lack of task-based intentional control of action
can aspects of utilisation behaviour be differentiated?
Riddoch et al. (1998)
cup aligned with left hand, pick up with that hand
or cup aligned with right hand, pick up with other hand
ES: 59 year-old nursery nurse, with cortico-basal degeneration
gradual onset of motor diffiuclites, problems including lack of control over her hands
including striking her aunt at dinner
she was aware of these gross errors, and tried to sit on her hands to control them
compatible conditions (same hand): 20/20 or 19/20
incompatible conditions (opposite hand): 3/20
even though the patient understood the task rule, could discriminate left + right (generates the overlearnt response to the stimulus, not the one she was supposed to)
cup turned upside down (less familiar to the patient)
was able to use her left hand to pick up the mug on the left, even though the handle was on the wrong side) 18/20
with cup-like object 16/20
ES right hand grasp responses:
affected by familiarity of object
affected by familiarity of object orientation
very difficult for her to over-ride competing stimulus response
can help by altering the stimulus (but the instructions remained the same each time)
if given both a black (distractor) and a white cup, never pick up the black mug
task: pick up the white object by the handle
minimal errors due to reaching to distractor
but many errors with reaching with the wrong hand
intention to select the object is relatively intact
but poor intentional selection of the correct action
i.e. stimulus selection is intact, but response selection is impaired
what kinds of representation are used as templates for object selection?
templates specifying perceptual attributes (Chelazzi et al 1993)
templates specifying affordance
bi-lateral damage: each hand was uncontrollable in different ways
MP 53 year old (aneurysm of right middle cerbral artery � right fronto-temporal lobe damage)
find the hammer (amidst objects on a table)
find the object you would use like this
easier, faster to select by specified action than by specifying the perceptual attributes of stimuli
separtion between the ability to select the stimulus and the ability to select the response
some complexities
timing factors in action
FK 30 years old = patient with symptoms of utilisation behaviour
former engineering student, suffered CO poisoning
bilateral damage to middle/superior temporal lobes and to medial frontal regions (archetypal frontal: very impulsive)
right handed � difficulty in controlling it
task: reach for the target with the hand matching its handle (distractor object present)
often picked up the distractor, not the target, with an incompatible hand (the action produced when distractor errors occur are very difficult to induce intentionally)
aiming for the distractor (right-orientated) but picks up the left-orientated target which is along the reach trajectory
internal and external control of selection
explored the Simon and the reverse-Simon effects
press button if object is on the left, or says �LEFT� etc.
reverse Simon - responding to the location of the stimulus, ignoring the meaning (or vice versa)
very slow if incompatible stimulus (e.g. the word �Right� on the left)
much faster if distractor present (larger perceptual load, perhaps enhancing the patient�s attention to the perceptual properties, which is what the patient has to respond to)
facilitates the reverse Simon-task (respond to location)
disrupts the Simon-task (respond to meaning and ignore location)
enhanced processing of perceptual attributes under conditions of perceptual load
automatic attraction of resources to perceptual processing?
functionally separable processes for the intentional control stimulus selection and the intentional control of response selection
intentional control of stimulus selection uses top-down templates for perceptual and action-response
how easy would it be to induce similar behaviour in normal subjects?
should be able to pick up at a smaller level in normal subjects, e.g. if give them a deadline, they generate errors, usually based on the visual rather than the semantic
ERPs
affordance
so is this evidence of overlearned responses, or a second agency (e.g. striking the aunt at dinner)?
Simon/reverse Simon effects (overlearnt S-R)