Lecture 3: The cognitive approach

Question 1

Four elements of experimental procedure

Answer 1

Manipulation.
What are we going to manipulate to alter behaviour.
Measure.
How will we quantify changes in behaviour relative to the stimulus.
Task.
What will the participant do.
Stimulus Selection Method.
How will stimuli be selected

Question 2

Cognitive Psychology

Answer 2

Donders (1868) Dutch opthalmologist measured reaction time: time between presentation of stimulus and person’s response to that stimulus

The time taken to make a decision enables us to infer something about that decision.

The longer it takes to make a decision the harder the task is.

If one task takes longer than another then we are better able to process the shorter task.

Question 3

Cognitive Measures

Answer 3

Reaction times
Eye movements (see Additional Material) or other actions
Accuracy

Question 4

Accuracy

Answer 4

Accuracy is a secondary measure in cognitive psychology.
Most tasks are designed so that the participant can do the task well with accuracy close to 100%.
This consistently high level of performance allows reaction time to be the primary measure of task difficulty.
Error trials are often rejected from analysis, participants may be rejected if they do not reach a certain level of performance.
Speed – accuracy trade off is a confounding factor – see later.

Question 5

Reaction time tasks: Simple Reaction Time

Answer 5

Simple Reaction Time
In simple reaction time experiments, participants respond as quickly as possible anytime a stimulus appears.
Generally the stimulus is known or in some way predictable.
The only uncertainty is regarding when the stimulus will occur.
Different conditions may produce longer reaction times.

Question 6

Example: Change blindness

Answer 6

(Look at Powerpoint for Image)

The stimulus is the change in the image – not the image itself.
The images changes in every trial.
The change sequence is manipulated to make changes easier or harder to detect.
Specifically a flash at the moment of change makes it hard to see the change.

Question 7

Reaction time tasks: Go – No Go

Answer 7

Go – No Go
Participants respond only when a particular stimulus appears and must NOT make any response when other stimuli appear.
Stimulus will vary from trial to trial.
Tests ability to discriminate stimuli – if the Go stimulus is very similar to the No-Go then the participant will be slow to respond.
Also tests the ability to inhibit response to the No-Go stimulus.

Question 8

Example Gambling Study

Answer 8

(Look at Powerpoint)

Question 9

Reaction time tasks: Choice Reaction Time

Answer 9

Choice Reaction Time
Participants presented to two types of stimulus and must indicate which is present.
Stimulus will vary from trial to trial.
Tests ability to discriminate between stimuli
Also tests biases towards or away from stimuli.

Question 10

Example Visual Search

Answer 10

(Look at Powerpoint)

The stimulus is the presence of a given target.
Some trails have the target, other not.
The participant must choose the appropriate response – ‘Present’ or ‘Absent’
Some targets harder to detect than others – this also depends on the distractors.

Question 11

Analysis: Reaction Time Distributions

Answer 11

Can’t have negative reaction times. Minimum somewhere around 300ms.
Can have some very long reaction times.
RT distribution positively skewed.
Take median RT rather than mean RT for each individual
Some people use “trimmed means”
Most studies ignore information apart from the ‘average’

Question 12

Speed Accuracy Trade Off

Answer 12

Luckily less common than you might imagine but very awkward to deal with when you get it!

Solutions
Can manipulate via verbal instruction to participants
Can manipulate via costs/ benefits of different types of responses e.g. have to repeat the trial if inaccurate
Can devise a measure that takes RT and accuracy into account (eg. efficiency = RT ÷ accuracy)
Can try to account for the problem statistically after data collection (ANCOVA)

Question 13

Subtraction measure: Difference in RTs between conditions.

Answer 13

Posner & Mitchell (1967). Task to judge whether 2 letters the same or different

Responses to AA faster than to Aa
AA requires only visual recognition whereas Aa requires finding the name of each letter
74ms worth of “extra” processing

Question 14

Dissociations: Different pattern of results between participant groups

Double dissociation: Groups have exclusive deficiencies

Answer 14

(Look at Powerpoint)

Question 15

Manipulation

Answer 15

Manipulation refers to differences in stimuli or experimental conditions that alter performance.
We will take Visual Attention as an example.
There are many ways in which visual attention can be manipulated to make a task easier or harder.
These have been adapted to explore interesting aspects of mental processing.

Question 16

Change Blindness

Answer 16

Manipulation:
A disruption (in this case a flash) at the time when the change occurs.
Compared with no disruption.
Task
Simple Reaction time.
There is one response to be made as soon as you see the stimulus (in this case the change).
Analysis
Need a second response to check the participant saw the change.
Ignore any incorrect trials.
RT can be very long so normally take the median.
Measure – Direct RTs or subtraction (disrupted – not-disrupted)

Question 17

Visual Search

Answer 17

Manipulation:
Distractors that make it harder to identify the target object.
Test with different numbers of distractors.
Task
Choice Reaction time.
There are two possible response, present or absent.
Analysis.
Ignore any incorrect trials.
Take median or trimmed mean of RTs in the different conditions.
Compare across different numbers of distractors and find search slope.
Search slope is effectively a subtraction measure

Question 18

Posner Cueing

Answer 18

(Look at Powerpoint)

Manipulation
Cueing. A cue stimulus is presented just before the target.
The cue can be valid or invalid.
Different sorts of cue are used.
Eg. Exogenous, Endogenous, ‘subliminal’, emotionally laden etc
The ability of the cue to drive attention is assessed.
Task
Choice reaction times – Choose location of stimulus.
Analysis
Median reaction times for each condition.
Measure
Subtraction: difference between valid and invalid gives and index for attentional drive.
Can also present as a double dissociation

Question 19

Dot Probe Task

Answer 19

Manipulation
Two images are presented just before a probe dot.
Typically once is salient the other not.
The probe dot can appear on either image (or location).
Congruent or incongruent with the salient image.
The ability of the images to drive attention is assessed.
Task
Simple or choice reaction times based on presence or nature of target.
Analysis
Median reaction times for each condition.
Measure
Subtraction: Difference between valid and invalid gives and index for attentional drive or bias.
Can also present as a dissociation

Question 20

Example 4: Stroop (e.g. Green, Corr and De Silva, 1999)

Answer 20

(Look at Powerpoint for Image)

Question 21

Stroop Task

Answer 21

Manipulation
Stimulus with two sources of information displayed.
Image (eg colour) conveys one response.
Text (ie words) conveys a different response.
Congruent trials both responses are the same.
Incongruent trials the two responses are different.
Task
Choice RT identify the text based outcome.
Analysis
Median reaction times for each condition.
Measure
Subtraction - difference between conditions.

Question 22

The Importance of Control

Answer 22

Any conditions compared should be as similar as possible in terms of everything except the thing which is being manipulated

So e.g. category decision task (fruit/veg):

		tomato		         tomato
		potato                         butternut squash

words same length, same number of syllables, but typicality of exemplars different since tomatoes normally eaten as veg. but is fruit. Both commonly found as compared to e.g. mangosteen vs. potato

Question 23

Summary

Answer 23

Cognitive methods have been used extensively to investigate attention but can be applied to a wide range of processes and behaviours: e.g. Memory (See Additional Material).
Measuring reaction time and accuracy in a variety of tasks can tell us something about how cognitive processes needed to perform a task are different.
Reaction time is a simple and effective test method that participants find easy to understand.
Stimuli of interest are typically highly visible and present for a long time. Although attentional probes and cues may be less obvious.
This leads to a need for strict control and instructions.
Speed accuracy trade-off can spoil or obscure results.