L09 - Decision Making Flashcards
Machine measuring eye movement
- 2 IR emitters with 1 central IR detector
- Shines 22 IR patches onto the front of the eye
- Highly reflective sclera will be sitting on one of the patches (depending on if the eye moves left or right) hence one reflective signal will be higher in one patch then the other when the eye moves
Saccadic latency – what is it? Compare with neuronal conduction during saccade initiation
- Delay between onset of visual target and saccade (when you move your eye)
- Latency much longer and more variable than neuronal conduction times or synaptic delays in shortest path to areas of brainstem involved in saccade initiation
Why is saccadic latency so long?
Low-level centres can quickly determine where object is but not whether it is worthwhile looking at. Hence, they hold it in check until higher-level processes decide suitability of target = oculomotor procrastination
*Latency therefore reflects decision-making time of higher-level centres
Model for latency data: LATER
Linear Approach to Threshold with Ergodic (randomness) Rate
Timing of latency changes with age and depends on the person but is around _ ms BUT it is true that ~ms is the time needed for info to reach colliculus – hence there is ~ ms of delay
180, 70, 100
Why “gratuitous randomisation”?
Output not determined even if input is = prevents responses being stereotyped
Behaviour therefore (partly) randomised:
- advantageous for outwitting opponents as they can’t predict what you will do (“game theory”)
- encourages exploration/discover/creativity
- Underlies illusion of free-will
Latency variability can be due to other factors such as?
- Sensory signals are noisy
- Variability in reaction time actually reflect time for accumulation of noisy signal to diverge significantly from background noise?
- Random-walk/diffusion models where accumulation of noisy evidence until threshold reached. It is based on signal detection theory
Key difference between Random walk model and LATER model
- No linear rise
- the smaller the signal, the longer it takes to accumulate
The higher the contrast of a visual target, the shorter (quicker) the reaction time – less time in stage one and more time in stage two
Two-stage model
2 sequential stages, whose latencies sum:
First stage = random walk = detection (collection of evidence)
Second stage = LATER = decision (verdict based on evidence)
Once first stage is complete, unit raises its hand and provides constant input signal to second (LATER) stage
When stimulus is difficult to detect:
first stage takes most time, so dominates overall behaviour
When stimulus easy to detect:
second stage takes most time
Why two stages?
Behavioural evidence When contrast (affects early detection stage) and prior probability (affects later decision making stage) simultaneously manipulated their effects appear to add linearly and independently
Philosophical evidence
Low level visual features may constitute evidence for competing hypotheses:
-Inappropriate for global decision parameters (e.g. expectation, urgency, etc) to act as low-level detection stage, therefore global decision parameters influence second stage ONLY
The “where/location” of the object info goes to ____ ____ (has oculomotor map) (low/high-level)
The “what/decision” of what to do with the object goes to the ____ (low/high-level)
Superior colliculus, low
Cortex, high
Increase in probability is a ____ in latency
Decrease
Initial visual activation of frontal eye fields (FEF) neurons does not distinuish between target and distractor but what happens eventually?
It diverges = detection stage
*Subsequently, there is a constant rise in activity of movement selective cell: saccade initiated after activity reaches constant threshold level
Latency is due to the movement processing stage after target discrimination
