Inferential tools for visual cognition

Problem 1 - Visual search

What conclusions might I be able to draw from the msec. data summarised below? What other data do I need to really make sense of these results?

Set sizeResponse 5 15 25

Cond. 1 absent 500 600 700present 450 500 550

Cond. 2 absent 500 500 500present 450 450 450

Problem 2 - Same/different visual imagery task

What conclusions can I draw from the % accuracy data summarised below?

Orientation15 45 75

Horizontal 100 100 75Vertical 100 80 50

Neurophysiology

• Single cell recording

• Brain imaging (fMRI, PET)

What kinds of neurophysiological questions does it make sense to ask?

• What cells respond to specific stimulus properties?

• How selective are the responses of cells?

• How are networks of cells organised?

• What brain regions process specific information?

• How are networks of brain regions interconnected?

Neuropsychology

• Dissociation

• Double dissociation

What neuropsychological questions does it make sense to ask?

• Damage to which areas leads to what deficits?

• Which processes are functionally independent of each other?

Psychophysics

• Measures of sensitivity

• Thresholds (e.g. method of limits)

• Signal detection theory (ROC curves)

Stimulus (Hz)

24 y23 y y22 y y21 y y20 y y y19 y y y y18 y y y y y17 y y y y y16 y y y y y y15 y n y y y y y y y14 n n n n n n y n n13 n n n n n12 n n n n n11 n n n n10 n n n9 n n8 n n7 n n

T= 14.5 15.5 14.5 14.5 14.5 14.5 14.5 13.5 14.5 14.5Mean= 14.5 sd=.45

Determination of lower limit of audible pitch, (Titchener, 1910)

What psychophysical questions does it make sense to ask?

• What is the detection threshold for a stimulus under specific conditions?

• How sensitive are observers to specific parametric manipulations?

Behavioural measures

• Introspection

• Reaction times (Mental chronometry)

• Errors

Reaction times:

Transduction of physical energy into neural code

+

Transit time to brain area (areas) where decision can be made

+

Decision processing time

+

Transmission of decision to muscles for action

+

Muscles to complete response

Decisions:

Relevant stimulus processing

Strategic response concerns

(time pressure, accuracy, etc)

What questions does it make sense to ask from behavioural measures?

• How do task factors affect response times/error rates?

• How do strategic factors affect response times/error rates?

Cognitive psychology

• Careful consideration of representations and processes underlying behaviour.

• No assumptions regarding brain-behaviour relationships.

What kinds of questions does it make sense to ask in cognitive psychology?

• What predictions can be made from models to behavioural measures?

• Do the effects found in the behavioural measures match those predicted by the models.

The relationship between models and data can be formalised as:

Q. What happens when prediction from model is not supported by the observed data?

1) A set of observations Ei obtained under intial conditions c 1, c 2, c 3...cn

constitutes relevant evidence in support of hypothesis H and related auxiliaryhypotheses a1, a 2...and in model M provided that E i can be derivedcomputationally from H in M and the specified initial conditions.

Notes:2) Assumption of universality. Groups are valid only to the extent that M can be

true of all individuals within the group.3) What happens if Ei does not occur? Do we reject M? H, or auxiliary, could be

false so only reject if you have a better alternative.4) Initial conditions known independently of Ei

How can cognitive models be used.

• As coherent explanations of mental life in their own right.

• As inferential tools for neurophysiological, neuranatomical, neuropsychological and psychophysical approaches. Given a particular hypothesis concerning the relationship between behaviour and brain, a specific model might imply the existence of particular neural modules.