Post on 11-Jan-2016
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C81MPR Practical Methods (Lab 1)
Dr. Danielle Ropar & Dr. Jonathan Stirk
Stroop (1935)
Stroop (1935) Exp’t 1: had subjects read out loud the names of colour words printed on cards in different coloured inks.
Each card had 100 colour-names on it. Words in the experimental list were all incongruent
(e.g., RED written in YELLOW: RED) The control-condition cards were identical but all
the colour-names were written in BLACK ink. The results showed no differences in time taken to
read the word lists for the control and experimental groups
So: when word name and word colour are incongruent, naming the word is not interfered with
However!
Stroop (1935) Exp’t 2: had subjects read out loud the colour of the words printed on cards
For the control condition he used coloured squares in the list
This time the experimental group took longer than the controls
So: When the colour of the ink and the word name are incongruent (don’t match), the word name interferes with naming the ink colour.
Stroop variant
In a variation of Stroop’s experiment, we can present subjects with colour names in either the matching (congruent) or non-matching (incongruent) ink.
Congruent (e.g., RED written in RED: RED) or Incongruent (RED)
When subjects name the colour of the words they are slower on incongruent trials than on congruent ones
This is known as the STROOP EFFECT
Beware the Stroop!
It’s everywhere!
Try it yourself!
Try naming the colour of the ink for the words below as quickly as you can:
RED
BLUE
GREEN
YELLOW
CONGRUENT CONDITION
RED
BLUE
GREEN
YELLOW
And again…
Try naming the colour of the ink for the words below as quickly as you can:
INCONGRUENT CONDITION
Independent & dependent variables This design uses the experimental method
(see stats lecture 2). In this experiment we have 1 IV which we are manipulating at 2 levels– Congruency
Congruent vs. Incongruent Our DV is what we actually measure and is
normally the time taken to read lists or reaction time to make a response (in the exp’t you are about to do)– Time is normally measured in seconds or
milliseconds (thousandths of a second). We will use milliseconds (msecs) in today's experiment.
– This DV uses a RATIO scale of measurement.
Explaining the Stroop effect There are a number of theories used
to explain the Stroop phenomena Two are:
–Relative Speed of Processing –Parallel Processing
There are others which we will not discuss today
Relative speed of processing In the incongruent condition, the two dimensions of
the stimulus (colour and word) are involved in a 'horse race' competing to see which can get to elicit the response (response competition)– The word name response often wins the race because it is
assumed that reading a word is faster than naming a colour
Then there is a competition for control of the response – This takes time which accounts for the Stroop Effect
Button PressInk ident.Slow
Word ident.
Decision
Fast
Speed of processing
Both attributes arrive at different times to a decision making component which has limited capacity and can only process one input at a time (serially)
PROBLEM: This theory cannot account for the Reverse Stroop effect (reversal of interference: colour of word ink interfering with word naming) –see next slide
Speed of processing account doesn’t predict reverse interference
Button PressInk ident (BLUE) Slow
Word ident (RED)
Decision
Fast
So, in the reverse task you have to name the WORD
In the incongruent pairing: RED
Button PressInk ident (RED) Slow
Word ident (RED)
Decision
Fast
In the congruent pairing: RED
Parallel processing
The general idea is that potentially relevant evidence is collected until a decision is reached about which response to make. – When there is a conflict between different sources of
evidence it takes longer to reach a decision. The Parallel processing utilises the strength of the
pathways that convey information that is important rather than the speed of processing. – Pathways that have become automatic have greater
strength and this leads to the asymmetry that produces the Stroop effect.
This model appears to be able to handle all the empirical findings related to the Stroop effect.
Parallel processing
Button Press
Ink ident.
Word ident.
Decision“accumulator”
Information arrives simultaneously
Stronger pathway
Weaker pathway
Separating the theories If we reverse the task (recognise word and ‘ignore’ ink
colour) what do the two theories predict?
Speed account: There will be no reverse Stroop effect because word form would have been processed and decision made before ink was recognised
Parallel systems: There will be a significant, but weaker, effect because the two signals are being processed (even though the ink signal is weaker). So we might expect to find some reverse interference
A journal article
HALF A CENTURY OF RESEARCH ON THE STROOP EFFECT - AN INTEGRATIVE REVIEW
MACLEOD CMPSYCHOLOGICAL BULLETIN 109: (2) 163-203 MAR 1991
Abstract:
The literature on interference in the Stroop Color-Word Task, covering over 50 years and some 400 studies, is organized and reviewed. In so doing, a set of 18 reliable empirical findings is isolated that must be captured by any successful theory of the Stroop effect. Existing theoretical positions are summarized and evaluated in view of this critical evidence and the 2 major candidate theories-relative speed of processing and automaticity of reading-are found to be wanting. It is concluded that recent theories placing the explanatory weight on parallel processing of the irrelevant and the relevant dimensions are likely to be more successful than are earlier theories attempting to locate a single bottleneck in attention.
Conducting a literature search
Basic steps
Define the enquiry Gather Background Information Carry out the Search Locate the References Compile a reference list of cited
material
Define the enquiry
There are two basic questions that need to be answered– What kind of information is needed?– How much detail is required?
Gather background information Read textbooks relevant to the
area Use subject dictionaries and
encyclopaedias Look up any reference material
that you have already been given Generate a list of keywords with
which to search databases– E.g. Stroop task
Carry out the search & locate references There are both printed and
electronic databases of references
Printed databases, e.g.– Psychological Abstracts
Electronic resources, e.g.– PsycINFO, ISI Web of Science (WOS)
Both require you to log on to your University account
– University of Nottingham Library
Compile a reference list Remember two points when
referencing published material– Give sufficient detail to enable anyone to
identify the book or article to which you are referring
– Give the references in a consistent form Normally the APA format (see APA citation guide
at Ohio State University) Use secondary citations for work that you
haven’t read directly