Exam #1 Flashcards
What is perception?
Fundamental freedom (and limitation), biological process that provides us with useful info about objects and events in our world that can be used to guide our cognitions and actions
Perception is self-referenced
Object and events are perceived relative to perceiver’s perspective
Perception is active
Perception guides action and action informs perception (to see, we look)
Perception is constructive
Vision tries to find “meaning” in everything we see, fills in the gaps (ex: finds faces)
Perception is relative
Depends on context (ex: same size middle circle surrounded by different sized outer circles)
Perception is invariant in the face of changing stimulation
“Perceptual constancy”: perception remains constant even when the associated sensory data varies
Perception changes in the face of unchanging stimulation
Ex: can see two different images in one image-optical illusions
Perception enhances the novel and ignores the unchanging
Certain things stand out while things that don’t change are ignored (habituation)
Perception is guided by expectations and by context
We always try to expect things (ex: moon and its changing size, camel photo with shadows)
Perception can be educated
Shown ambiguous photos, only see it when you have knowledge of what it is
Perception is an intelligent, adaptive process
Takes limited sensory data, and using built-in assumptions, deduces what in the world gave rise to that sensory data
Perception involves competing demands
- Sensory vs resolution
- Discrimination vs generalization
- Grouping vs segmentation
Sensitivity
Being able to detect “faint” signals, smallest amount of difference
Resolution
Being able to distinguish among multiple signals (eg: their location), smallest unit of measurement that can indicated by an instrument
Grouping
Combining elements based on their common features
Segmentation
Picking out a given element from a background of similar events (ex: can see the letter B behind a dark background)
Generalization
Categorize based on common feature (ex: calls all adult men “dad”)
Discrimination
Distinguish among similar objects, organism responds differently to 2 stimuli (ex: call only your father “dad”)
Is perception more useful or accurate?
USEFUL
What determines which parts of the world are sampled by perception?
Portions of the environment are perceptually important to different organisms (ex: bees can see UV light) based on habits, habitats, time most active
Psychophysics
Quantitative branch of study of perception, examines relations between observed stimuli and responses and reasons for those relations (ex: can see dimmer spot of light in darker env)
Phenomenology
What do things look, sound, smell, like? Study of consciousness and objects of direct experience (ex: moon looks larger when on horizon)
What is interpretation of psychophysical data strongly influenced by?
Known anatomy and physiology of sensory systems
What do psychometric functions look like?
Sigmoids, almost always 1 experiment
Absolute threshold
Lower limit of perception, weakest stimulus that can just barely be detected
Difference threshold (JND)
Smallest reliably discriminable difference between 2 stimuli (AKA just noticeable difference) (ex: forgot glasses)
Point of subjective equality (PSE)
Magnitude of one stimulus at which it is perceived as equivalent in magnitude to another
Weber Fraction
JND divided by magnitude of the standard
Weber’s Law
Increases in intensity that are just noticeably different to an observer are constant fraction of stimulus intensity
Method of adjustment
Person (subject) adjusts stimulus to value where it is barely detectable (absolute threshold) or adjusts one stimulus until it matches another (PSE) or differs from another (JND)
Method of limits
Experimenter changes stimulus by small amounts to find point where person’s judgment of stimulus first changes
Method of constant stimuli
Present stimuli at various “levels”; person responds (Y or N) following each presentation, generating a psychometric function
Staircase method
Adaptive search for threshold, designed to converge to certain threshold value
- Correct responds=harder
- Incorrect response=easier
What is hysteresis?
“Path dependence”, problem in method of limits, threshold value will differ dependent upon whether experimenter starts with dim or bright light
2 types of staircase methods
- Fixed step size
2. Adaptive step size (asking where someone is from analogy)
Signal Detection Theory (SDT)
Measure ability to differentiate between stimulus and noise, measure sensitivity independently of criterion
Perceptual decisions are influenced by many factors (6)
- Strength of signal relative to background level of noise
- Person’s sensitivity to signal
- Relative frequency of occurrence of signal
- Person’s level of motivation
- Costs associated with hits and false alarms
- Personal biases (individual differences)
Hit
Signal was present, person says yes
Miss
Signal was present, person says no
Correct rejection
Signal not present, person says no
False alarm
Signal not present, person says yes
Discriminability
How well the observer can separate the presence of signal from its absence (overlap between 2 distributions)
Receiver Operating Characteristic (ROC)
Plots hits against false alarms as criterion moves
Sensitivity (d’) depends on (3)
- Signal strength
- Noise strength
- Observer sensitivity
How to make visible, “invisible” (6)
- Degrading visual stimulation
- Crowding
- Masking
- Motion induced blindness
- Binocular rivalry
- Bistable figures
Criterion depends on (3)
- Personal bias
- Cost/benefit factors
- Signal frequency
Factors involved in what we see (3)
- Light sources
- Surface reflectance
- Eye sensitivity
4 ways eyes are constantly in motion
- Saccades
- Pursuit/tracking movements
- Vergence movements
- Microsaccades
What is the curvature of the flexible lens changed by?
Ciliary muscles
Accommodation
Ability to increase the curvature of the lens
Presbyopia
Flexibility of lens is reduced, harder to bring near objects to focus
Axial myopia
Nearsightedness caused by lens being too far from retina
Refractive myopia
Lens-cornea system is too powerful for normal length of the eye
Transduction
Light changes molecular properties of photopigments, which changes electrical states of these cells
How many rods vs cones?
Rods: 120 million
Cones: 5 million
Border enhancement
Borders are the main cue for objects
Strict definition of receptive field
Area of the retina over which a ganglion
cell is sensitive to light stimulation. i.e., an area of the retina that the cell monitors.
Practical definition of receptive field
Area of the world over which a
ganglion cell is sensitive to light stimulation. i.e., an area of the world that the cell monitors.
Simple cells
Respond to bars of light in a particular orientation and a particular location within the receptive field
Complex cells
Respond to bars of light in a particular orientation moving in a specific direction
Hypercomplex cells
Respond to bars of light in a particular orientation, moving in a specific direction, and of a specific line length
What 3 quantities characterize gratings?
- Spatial frequency
- Orientation
- Contrast
Orientation tuning curve
In simple cortical neuron, relation between orientation of a bar or grating stimulus and firing rate of the cell
Spatial frequency tuning curve
Relation between frequency of grating stimulus and firing rate of cell
Hypercolumn
Complete feature detector for very small part of visual field. Contains color cells, orientation cells, disparity cells, motion cells
Contrast sensitivity function (CSF)
Plot of the threshold contrast to detect the grating as a function of spatial frequency
