PY1501.4 ~ {Methods in Cognition and Perception}
what did Donders (1868) measure and what can we infer from it
dutch opthamollogist measured RT [time between presentation of stimulus and person's response to that stimulus]
the longer it takes to make a decision the harder the task is
4 elements of experimetal procedure
manipulation[what are we going to manipulate to alter behaviour]
measure [how will we quantify changes in behaviour relative to stimulus]
task [what will the participant do]
stimulus selection method [how will stimuli be selected]
cognitive measures and tasks
RT + accuracy + eye movements / other actions
eye, hanf and body movement tracking can measure a number of properties but often the time taken to initiate movement [ i.e RT] is used
accuracy
secondary measure in cognitive psych
most tasks are designed for close to 100% performance
makes RT the primary measure of task diffiuculty
error trials rejected from analysis
participants may also be rejected
speed accuracy trade off is cofounding variable
reaction time tasks
simple reaction time
in simple RT experimemts, participants respond as quickly as possible when a stimulus appears [generally the stimulus is known or in some way predictable] so the only uncertainty is regarding when the stimulus will occur
change blindness
stimulus is the change [not the image itself]
the imahes change in every trial, change sequence is manipulated to make changes harder to detect [specifically, a flash at the moment of change makes it hard to see change]
RT tasks: go - no go
particpants only respond when a particular stimulus appears, stimulus will vary from trial to trial and this tests ability to discriminate stimuli and inhibition [if participant is addicted to something might find it harder to 'not go' and easier to 'go']
gambling study
participants must 'go' if stimulus shows a gambling activity but 'no go' for neutral stimuli [these are rare] and in this case we expect gamblers to respond more quickly than non-gamblers
choice RT
participants presented to 2 types of stimulus and must indicate which is present. stimulus will vary from trial to trial, tests ability to discriminate between stimuli and attentional bias towards or away from stimuli
attentional bias
tendency for individuals to selectively focus on certain stimuli [often related to their emotions, beliefs ir current concerns] whil ignoring other info. this bias can affect how people process info and may influence behaviour, particularly in areas like anxiety, depression and addiction
visual search
2 letters presented [T + O] and the target stimulus is a red T so in some trials its there in others its not, and the participant must s=choose appropriate response [present / absent] however some targets are harder to detect than others - this also depends on the distractors
examples of choice RT experiments
to say if 2 things are the same or diff
to categorise an object [veg / fruit]
to respond whether a word / object is real
to detect an object [find a B amongst many P's]
distribution of RTs
RTs tend to be skewed, but we typically take the median of each participamts RT in each condition, we do this because the distribution of medians is less skewed
Posner & Mitchell (1967)
subtraction measure - task to judge whether 2 letters are the same or different
results showed responses to AA were faster than Aa because AA requires only visual recogntition whereas Aa requires finding the name of each letter [subtraction: 620-540=80ms worth of extra processing
dissociation
phenomenon where 2 variables / set of results do not follow the same pattern or show a distinct separation, despite being part of a related process or underlying structure
cognitive dissociation
when diff cog abilities diverge + how they are affected by various factors like task difficulty / neurological conditions / age. a test could be done with healthy participants vs patients with brain damage [would show dissociation between groups]
why are dissociations [between participant groups] useful
they can indicate underlying psychologival / neurological processes, differences in perception, variability in behaviour due to external factors [age, cultural influence, disease] helps us gain a deeper understanding of how diff factors shape human cognition, behaviour and neural function
Ellis (1981)
dissociation in dyslexia [used a varaition of Posner & Mitchel task] where the visually identical [AA] dyslexic group mean= 960ms vs 933ms controls and for the phonologically identical [Aa] dyslexic group mean 1156ms vs 1039ms for controls
double dissociation
when groups with diff neurological conditions or diff brain damage show diff, mutually exclusive abilities and deficiencies. the key idea is that impairments in each group occur in opp ways on 2 diff tasks [ so our double dissociation provides stronger evidence for the independence of the 2 functions - shows function can be impaired without affecting the ither and vice versa]
classic crossover
specific pattern of results that is typically observed when comparing 2 experimental conditions across 2 diff participant groups, pattern is essential in demonstrating that 2 functions are independent + involve separate neural mechanisms
classic crossover in double dissociation
involves 2 groups [group 1 & 2] each performing 2 tasks [task A & B] under diff conditions and the pattern of results might look like: Group 1 showing impairment on task A but perfoming normally on task B and the opp for Group 2. this crossing of results indicates that the 2 tasks are independent of each other.
what does classic crossover in double dissociation suggest
that each task relies on diff neural systems / cognitive processes + brain systems or functions underlying the 2 tasks are distinct, as evidenced by the differing patterns of impairments in the 2 groups
speed acuracy trade-off
we can go faster if we are less accurate [ in a choice reaction task just pressing any button we'll go faster but get more wrong answers]
accuracy should be over 95% in all conditions with no significant diff between conditions
solutions to speed accuracy trade-off
verbal instructions to participants
costs / benefits of diff types of responses [ have to repeat the trial if innaccurate]
devise a measure that takes RT and accuracy into account
account for the problem statistically after data collection ANCOVA
experimental manipulation [in cognition]
diff in stimuli / experimental conditions that alter performance
visual attention - helps researchers understand how the brain selects relevant imfo while ignoring distractions
common experimental manipulations of visual attention
the stroop tasks
posner cueing task
flanker task
visual search task
change detection
attentional blink
dot probe task
measures attentional bias
fixation cross on screen for around 500ms + 2 stimuli [ one neutral the other emotional / threatening] + a small dot [probe] appears in same location of 2 stimuli [participant responds to location of probe as quickly as possible] + measuring RT to probe
the stroop task
show participants names of colours but printed in diff ink colours [purple in blue ink] and the participants are assked to name the colour of the ink not the word itself. this tests selective attention cause the participants are forced to ignore the meaning of the word and focus om the ink colour
the posner cueing task
participants are shown a central fixation point a cue [arrow] is presented to direct attention to a specific location on the screen. after a short interval the target reappears in one of 2 locations [valid or invalid]. this investigates spatial attention: how attentionis directed to locations in the visual field and how it affects RT
the flanker test
selective attention with distractors
participoants asked to focus on a target stimulus surrounded by other stimuli [flankers-which can either ve congruent, incongruent or neutral with the target]. task tests ability to focus on a target stimulus while ignoring distractors.
search slopes / efficiences
the rate at which RT increase as number of items in the visual search array increases, it is a key measure of how difficult or efficient the search process is
what do search slopes show us
steep slope - indicates the RTs increase quickly as the number of items in the search array increases which suggests the search is innefficient or serail meanaing participants examineeach time individually to find the target
history of psychophysics
Gustav Fechner developed the term psychophysics in 1860 when exploring methods of relating 'matter to mind' this set the foundations for psychology as a science
psychophisics definition [ Bruce V, Green PR, Georgeson MA (1996). Visual perception (3rd ed.).Psychology Press
The analysis of perceptual processes by studying the effect on
a participant’s experience or behaviour of systematically varying the properties of a stimulus along one or more physical dimensions.”
what is psychophysics
subfield of psych that deals with the relationship between physical stimuli and the psychological experiences or perceptions that these stimuli evoke [studeies how we perceive the world base on the physical properties of stimuli and how these stimuli transalte into sensory experiences]
4 elements of a psychophysics procedure
manipulation [masking + facilitation / priming + contrast effects + adaption]
measure [percent correct - thresholds + bias- +appearance - point of subjective equality]
task [single interval + 2 alternative forced choice + single interval symmetric choice]
stimuls selection method [constant stimulus + adaptive + method of limits + adjustment]
cognitive psych
mental processes
stimuli usually very obvious and present for a long time
stimuli oftwm complex + naturalistic
care about stimulus interpretatio
primary measure is RT, accuracy is the second measure
stimulus selection straightforward
psychophysics
sensory processes
stimuli usually very subtle and present for a short period of time
stimuli often very simple and stylistic [not always]
care about stimulus composition
prime measure accuracy RT is ignored
stimulus selection complex - adaptive varies between people
visual psychophysics
study of the relationship between physical stimuli and the perceptions. produced. studies help understand how the brain processes visual info and are fundamental in fields
contrast sensitivity
the ability to detect diff in luminance between an object and its background, esp when contrast is low, focuses on how well the visual system can perceive objects under varying lighting and contrast levels stimulus manipulation: diff spatial freq
psychophysics can be used to study any of the 5 senses: vision
intensity of light + contrast + colour + orientation + size + 3D Depth + motion + textures + objects / faces
psychophysics can be used to study any of the 5 senses: hearing
loudness of sound + pitch + direction
psychophysics can be used to study any of the 5 senses: touch
intensity of press + position on body + texture
psychophysics can be used to study any of the 5 senses: taste + smell
intensity + flavour + texture
intensity + odour
preferential looking tasks
contrast sensitivity adapted for infants [they can't verbally respond to stimuli]
used to study visual perception: 2 diff stimuli are presented side by side and measure the amount of time the child spends looking at each [assumption here is that they will spend more time looking at the one they find more interesting / engaging]
what can preferential looking task be used for
to study visual perception, investigate visual preferences, perceptual development, attentional bias [ colour discrimination, face recognition, objcet categorization]
detection threshold
minimum level of a stimulus that an individual can dtecet usually measured in terms of itensity. can vary based on each individual's sensory capabilities, enviro conditions + type of stimulus
how is detection threshols usually determined
through methods like method of constat stimuli, where a series of stimuli with varying intensities are presented, and the participant reports whether they detect the stimulus. the poiint at which detection occurs 50% of the time is often considered the threshold
how to not measure detection thresholds
subjective bias: allowing personal biases influence responses
inconsistent stimuli: that aren't controlled
overloading participant: presenting s too rapidly / often
lack of calibration
ignoring individual diff
not considering enviro factors
estimating threshold [ the psychometric function SI-TP]
analysis of individual's response probability varies with diff stimulus intensities [common approach is SDT signal detection theory such as SI-TP
SI-TP
stimulus intensity - true positive rate
si- represents varying lrvels of stimulus strength
true positive rate - probability that participant correctly detects the stimulus at each given intensity [hit rate: percentage of times participant correctly identifies stimulus]
two-alternative forced choice task [ spatial + temporal intervals
s - may appear in one of eo places and the participant must indicate which place the stimulus appeared in
t - may appear in one of two time slots and the participant must indicate which time slot stimulus appeared in
for both stimulus is present on every trial and there is no 'don't know' option
psychomteric function
mathematical curve that represents relationship between intensity if stimulus and probability of a subjects response used to quantify sensory perception and threshold estimation
2AFC
used to measure an individual's ability to discriminate between two stimuli. the participant is presented with two alternatives and must choose which one contains the target stimulus or is different in some way from the other.
system characterisation
the process of quantifying and understanding the behavior and performance of a system, particularly in terms of its input-output relationships, efficiency, limitations, and response to various conditions. involves determining how a sensory system (e.g., visual, auditory) or a technical system (e.g., electronic devices, algorithms) responds to different stimuli or inputs.
simultaneous masking and facilitation
a phenomena in perception, where the presence of one stimulus affects the detection or perception of another stimulus presented at the same time. often studied in the context of auditory and visual perception and are important for understanding the limits of sensory processing.
sequential masking and priming
where one stimulus influences the perception of another, but the influence occurs over time. Unlike simultaneous masking (which occurs when two stimuli are presented together), sequential effects depend on the timing and order of stimulus presentation.
difference between masks and facilitators
2 distinct types of stimuli that influence the perception of a target stimulus, but they have opposite effects
m - stimulus that impairs or hinders the detection or identification of a target stimulus
f - stimulus that enhances or accelerates the perception of a target stimulus
mask
a stimulus that impairs or hinders the detection or identification of a target stimulus. typically interfere with the processing of the target, often by overloading the sensory system or causing cognitive interference
facilitator
a stimulus that enhances or accelerates the perception of a target stimulus. improve the processing of the target by priming relevant sensory or cognitive pathways. can make the target easier to identify or react to by activating associated mental representations.
apperance by adjustment
used to measure a person's perception of a stimulus by asking them to adjust the stimulus until it appears to match a reference or achieve a certain perceptual criterion. [the white and gold dress]
measuring appearance using a single interval symmetric choice task
subject is asked to compare a single stimulus with a reference stimulus, and the task involves choosing one of two possible responses. used to measure a subject's perception of a stimulus
the psychometric function
key tool for modeling and analyzing how a subject perceives a stimulus in relation to its physical properties. describes the relationship between the physical intensity of a stimulus and the probability that a subject will respond in a certain way, such as detecting or identifying the stimulus.
PSE - point of subjective equality
a concept derived from the psychometric function, often used in magnitude estimation tasks or comparison tasks. the stimulus intensity at which two stimuli are perceived to be equally intense or equally different (depending on the task)
psychometric funtion and PSE in practice
the PSE can be found by examining the 50% response probability on the psychometric function. this is the point at which the subject is equally likely to respond in one direction (e.g., "yes, I detect the stimulus") or the opposite direction (e.g., "no, I don't detect the stimulus").
simultaneous presentation
where multiple stimuli are presented to a subject at the same time. In this approach, the stimuli can vary in intensity, frequency, or other properties, and the participant is asked to compare or respond to them simultaneously.
seqeuntial presentation
the presentation of stimuli one after the other over time, rather than simultaneously. in psychophysics, this method is used to study how the timing of stimuli affects perception.
tilt illusion (simultaneous tilt contrast)
visual phenomenon where the perceived orientation of a central stimulus is altered by the presence of surrounding stimuli. a stimulus (usually a line or bar) appears to be tilted in one direction due to the influence of neighboring lines or patterns that are tilted in the opposite direction.
how does the tilt illusion work
the central line or object is placed among several surrounding lines or patterns which are tilted in the opposite direction to the central line. as a result, the central line appears more tilted in the direction opposite to the surrounding stimuli. this occurs even though the central line's actual orientation remains unchanged.
method of constant stimuli
for determining a subject’s perceptual threshold—the point at which a stimulus is just detectable, or just noticeable difference (JND). in this method, a set of stimuli with varying intensities (or other relevant attributes) are presented to a subject, and the subject’s responses are recorded for each stimulus.
adaptive methods
used to 'home in' on a threshold / PSE levelstimuli value is adjusted up or down trial-by-trial according to participant responses [step size gets smaller as you progress] and they're called staircases.
transformed staircases
a variation of the staircase method used in psychophysical experiments to estimate a subject's perceptual threshold—the point at which a stimulus is detectable or the smallest difference between two stimuli that can be reliably perceived.direction of intensity adjustment is based on the subject's performance in the previous trial.
method of limits
present stimulus at low level - ask if the participant can detect it [yes or no] if not increase magnitude and try agian [keeping going until they say yes - ascending method of limits] or make stimulus weaker until you get a no [descending method of limits]
threshold
point at which they could first [or last] detect the stimulus usually you alternate between ascending and descending trials and average the thresholds otained
where is methods of limits typically used and why
clinical practice [hearing tests , eye test chart]
it is easy to carry out and requires relatively few trials
when used with yes/no task bias is an issue so its seldom used in experiments
method of adjustment
observer adjusts stimulus themselves until its detectable + it matches a sample or desired value – matching / PSE.
essentially a continuous single interval Yes-No or symmetric choice task.
threshold or PSE is the last setting made.
repeat a few times and average.
pros and cons of method of adjustment
very quick and easy + can only be used with adjustment tasks + the task and stimulus selection method are one and the same + results can be unreliable
subject to bias - adjustment task are logically similar to single interval tasks – hence bias + but for appearance measures we are not worried about bias.