3-1 behavioral and perceptual methods

cog sci research methods

Sensation and Perception

Sensation - Input about the physical world obtained by our sensory receptors; the physiological basis of perception 

Perception - How the brain selects, organizes, and interprets sensations; shaped by learning, memory, emotions and expectations

Sensation- kinds studies

• Vision 

• Hearing

• Taste 

• Smell 

• Pain 

• Touch 

• Balance 

• Movement 

What are the most studied sensations? 

• Vision and hearing

Kinds of perception in the reading 

• Unimodal vs multimodal - one sense, or several senses integrated into one percept 

• Depth perception - A 3D world inferred from 2D cues 

• Subliminal perception - stimuli below the threshold of awareness 

• Bottom up vs top down - built from sensory input, or shaped by knowledge and context 

Perception cant be observed directly - distal stimulus

an object or event in the world 

Perception cant be observed directly - proximal stimulus

the pattern that reaches the senses

Perception cant be observed directly - Percept

what we experience 

Psychophysics 

The study of how changes in a physical stimuls relate to what a person perceives

Absolute threshold

the minimum stimulus energy needed to detect a stimulus; for example, a candle flame about 1.6 miles away on clear night

Just noticeable difference (JND)

the smallest change needed to tell two similar stimuli apart 

Weber’s law

the JNG is constant fraction of the stimulus; foe weight about 5%, so 100g needs about 5g added

Caveat

Weber’s law is only approximate and less accurate near the detection threshold 

3 ways to measure a threshold

• method of limits

• methods of adjustment

• methods of constant stimuli

Method of limits

procedure - Intensity raided or lowered step by step until the observer reports a change; ascending and descending  series averaged

strength - Accurate

weakness - Time - consuming 

Methods of adjustment

procedure - Observer adjusts the stimulus (ex: with a slider) until it is just perceptible

strength - Fast; useful when attention is limited

weakness - Less accurate

Methods of constant stimuli

procedure - Many intensities presented in random order; threshold = intensity detected 50% of the time

strength -

Most reliable; removes habituation and anticipation errors

weakness - slowest

Why build illusions? 

they let scientists test how the perceptual system works by seeing when and how it gets things “wrong”

Putting illusion ex - Ebbinghaus illusion

Ex: “You and an equally skilled opponent are putting, but their hole is 10% bigger. Unfair, right?”

• “Now the holes are the same size, but theirs only looks 10% bigger. Is that still an advantage?”

Setup: an overhead projector cast a ring of circles around a putting hole. Some participants saw small circles around the hole, others large ones. The hole itself never changed size.

• This is the Ebbinghaus illusion: the surrounding circles change how big the hole looks.

Ebbinghaus illusion variables and design

Design and task 

• A ring of circles is projected around a 2-inch hole (half a regulation hole)

• 11 small circles make the hole look bigger; 5 large circles make it look smaller

• Putt from about 11½ feet: 10 putts with each ring

1. Whats the IV? 

• Size of the surrounding circles (small vs. large)

2. Whats the DV?

• Number of putts made out of 10 

3. Same order for everyone? 

• No: half saw large circles first (counterbalancing) 

4. Did the illusion work? 

• About 10% more putts when the hole looked bigger 

Basically the goal is to see if people putt better when they perceive the hole as larger or smaller 

Signal Detection Theory

• explains how people decide whether a stimulus is present when they can’t be sure

• Key idea: every “yes” or “no” depends on 2 separate things: 

  • 1. how well the person can tell the stimulus apart from background noise (sensitivity)

  • 2. how willing they are to say “yes” (response bias) 

Why a single threshold is not enough

Rare signals - World War II radar operators had to detect

infrequent enemy signals; Mackworth (1950) studied how vigilance holds up

• Watching for rare events makes concentration lag

Defining awareness - It is hard to establish the threshold for consciousness, or even which kind of threshold matters

• Cheesman & Merikle distinguish objective from subjective thresholds

The problem  An operator says “no signal” when one was there. Was it too hard to detect, or was the operator reluctant to raise a false alarm?  A threshold cannot tell these apart

Target vs foil

Target - what person is trying to detect 

Foil - anything that isn’t the target but might be mistaken for it 

Ex: someone is looking for angry faces.

• Targets: angry faces.

• Foils: non-angry faces.

Why errors happen: targets and foils can be perceptually similar, and noise comes from inside (sensory processing) and outside (the environment)

Target vs foil possible outcomes

	Responds “target”	Responds “foil”
Target present	Correct detection  (benefit)	Miss (cost)
Foil present	False alarm  (cost)	Correct rejection (benefit)

The decision is a choice under uncertainty, not just a readout of what was sensed.

Sensitivity vs response bias

Sensitivity (d′): the ability to discriminate targets from foils; higher sensitivity when foils are less similar

• how well you can tell things apart

• the distance between the curves

Response bias: the tendency to call stimuli targets - how readily you say “yes

Criterion for response bias

where the criterion sits.

• Liberal, criterion moved left: says “target” readily. More correct detections, but more false alarms.

• Conservative, criterion moved right: says “target” reluctantly. Fewer false alarms, but more misses.

• Neutral: in between.

Graph describes how “target-like” something seems on a given trial

Red line is the criterion: the person’s cutoff.

• Evidence above it gets “target”; evidence below it gets “foil.”

Reaction time paradigm 

an experiment that uses how quickly (and how accurately) people respond to infer what is going on in their minds.

Logic: if one condition makes people slower or less accurate than another, the extr time reveals extra mental processing.

The Stroop task: measures interference in time 

Control trial - name the ink color of a row of Xs  Incompatible trial - Name the ink of a conflicting color word

Finding: naming the ink color takes longer when it conflicts with the word (Stroop, 1935)

• Logic shared by today's RT paradigms: compare a conflict condition with a control; the extra time reveals processing of information that was meant to be ignored

  • Extra time - processing extra/excess information (interference)

The flanker task: interference in space 

Control trial - Flankers match the target Incompatible trial - Flankers match the other target

Task: respond quickly to the center letter (e.g., S = left hand, H = right hand) and ignore the flankers (Eriksen & Eriksen, 1974)

• Finding: responses are faster and more accurate on congruent than incongruent trials

• Explanations: attention works like a spotlight or zoom lens but cannot fully block nearby flankers, so competing responses are activated

Priming

• what comes first shapes the response

Definition: a prime precedes the imperative stimulus; it can be the same as, or different from, some aspect of that stimulus

• Status: priming studies have been popular in recent attention research

• Link to thresholds: late-selection models hold that unattended input is processed for meaning, consistent with subliminal perception, which is why awareness of the prime matters

Prime, imperative stimulus, response

Prime

• presented first

Imperative stimulus

• the one the participant responds to

Response

• measured, e.g., speed or accuracy
  
  

Eye tracking 

• Method that record where a person looks, for how long, and in what order 

• Researchers use to infer where attention goes and how long processing takes

Eye tracking - Data quality: 

• Sampling frequency: samples per second, from about 30 to 2000 Hz

• Accuracy: distance between true and estimated gaze

• Precision: how well repeated measurements agree

Eye tracking - Three set ups:

• Tower-mounted: chin and forehead rest

• Remote: camera at a distance; head moves within a range

• Head-mounted: worn, moves with the head

Looking is not the same as seeing 

• What it records: people make saccades (rapid movements of both eyes simultaneously) several times per second to bring new areas onto the fovea; eye tracking shows what they look at, for how long and in what order
  
  

• The inference: fixation durations may estimate processing time and fixation locations may approximate attention, but only under an explicit eye–mind assumption
  
  

• Evidence of the gap: drivers on a phone were less likely to later recognize objects they had looked at (Strayer & Drews, 2007)

• Design advice: if a research question does not need an eye tracker, leave it out

• We never observe perception or attention directly;

• every method infers them from behavior

Thresholds mix ability and willingness to respond;

•  signal detection theory separates sensitivity from bias

Stroop, flanker and priming share one logic:

compare a condition against a control and read the difference

Eye tracking shows where and when people look

• not what they process