PSYC 105 - CH 3-4: Perception

Akinetopsia

* unable to perceive motion
* cannot tell if movement is occurring
* cannot see the “in between” when objects are in motion

Rods

* sensitive in low light
* lower acuity
* color-blind
* periphery of the retina

Cones

* Need more light
* higher acuity
* color-sensitive
* in the fovea

Visual system

light to perception

* In the eye:
* photoreceptors
* bipolar cells
* ganglion cells and the optic nerve
* int he thalamus:
* Lateral geniculate nucleus (LGN)
* In the cortex:
* V1: the primary visual projection area, or primary visual cortex, located in the *occipital lobe*
* if damaged = “blind”, no sight

Lateral inhibition

a neuron’s response to a stimulus is inhibited by the excitation of a neighboring neuron

* occurs in cells in the retina
* each active cell inhibits its neighbors
* **Emphasizes the “edge” of the stimulus → “creates a contrast in stimulation that allows increased sensory perception”**

Receptive field

the size and shape of the area in the visual world to which that cell responds

* on-center/off surround cell
* stimulus in center leads to fast firing rates
* stimulus in surrounding are leads to slower firing rates (relative to baseline)

Edge detectors

each cell will respond to a vertical, or horizontal light respectively

* the receptive fields of some visual neurons are lines of particular orientations

binding problem

parallel processing splits up processing of our world → but we do not see the worlds as disjointed

spatial position

helps solve the binding problem

* reassembling of pieces references position

neural synchrony

helps solve the binding problem

* the rhythms of neurons that are firing in response to the same item (some for color, some for motion, etc.) tend to be in sync

Attention binding

critical for the binding of visual features

* when ________ is overloaded, people will make conjunction errors
* ex: seeing a blue “H” and a red “T” but reporting a red “H”

sensation

absorbing raw energy (e.g., light waves, sound waves) through our sensory organs

* for the most part, everyone has the same ___ to the same stimulus

Transduction

conversion of this energy to neural signals

Attention

concentration of mental energy to process incoming information

perception

selecting, organizing, and interpreting these signals

* the process of recognizing, organizing, and interpreting information from senses
* Not an exact copy of “the world”
* based on our past experience and expectations

Bottom-up processing

when the environment (stimuli) influences our thinking

* perception may start with the **senses**
* incoming raw data
* energy registering on receptors

Top-down processing

when our thinking influences how we see (understand/perceive) the environment

* making inferences based on context, guessing from experience, and basing one perception on another
* perception may start with the **brain**
* person’s knowledge, experience, and expectations shape perception
* occurs quickly, automatically

Recognition-by-components (RBC)

bottom-up processing

* we perceive objects by perceiving elementary features
* Geons: three-dimensional volumes
* objects are recognized when enough information is available to identify object’s geons

geons

* discriminability: ____ can be distinguished from other geons from almost all viewpoints
* Resistance to visual noise: ______ can be perceived in “noisy” conditions
* distinctiveness: 36 different _______ have been identified

Helmholtz’s Theory

theory of unconscious inference

* we infer much of what we know about the world
* likelihood principle: we perceive the world in the way that is “most likely” based on our past experiences

Perceiving size

bottom-up processing

* the size of the image on the retina

Top-down processing

* the perceived distance of the object
* the size of the object relative to other objects in the environment

Depth perception

the ability to see things in three dimensions (including length, width and depth), and to judge how far away an object is

* occurs even when looking at 2D images
* is present, at least in part, at birth in humans and other animals

Binocular cues

depth cues that require the use of two eyes

Retinal disparity

used to perceive depth between two near objects by comparing the different images from both retinas

* is a bottom-up cue of depth → it is not based on knowledge about the world

Monocular cues

depth cues available to either eye alone

* are top-down cues of depth → they are based on the knowledge you have about the world

Includes

* relative size
* interposition
* relative motion
* light and shadow
* linear perspective

Constancy

things look different depending in the angle, distances, and lighting but our perception is constant

Perceptual _____

* Size
* Shape
* Brightness
* Color

Size constancy

we perceive the size of an object as constant from different distances

* however, context matters (ex: moon illusion)

Shape constancy

even though the shape of the door on our retinal image differs, we see the true shape of the door as unchanging

Gestalt Laws of Perceptual Organization

reflect experience, are used unconsciously, but may be occasionally misleading

* similarity
* proximity
* good continuation
* closure
* simplicity

Form perception

the process through which the basic shape and size of an object are seen

* figure-ground: organization of visual field into objects that stand out from their surroundings
* grouping: the perceptual tendency to organize stimuli into meaningful groups (gestalt principle)
* utilizes both bottom-up and top-down perception processes

good continuation

law of continuity

* we tend to see shapes/lines as being continuous even when occluded

simplicity

law of good figure

* every stimulus pattern is seen so the resulting structure is as simple as possible

similarity

similar things appear grouped together

proximity

things near each other appear grouped together

closure

we tend to perceive closed figures rather than incomplete ones

object recognition

process through which the object is identified

* utilizes both bottom-up and top-down perception processes
* recognition through **features**: small elements that result from the organized perception of form
* ie: visual search task

Serial search

search every stimulus one by one for target

* RT depends on display size

Parallel search

target stimulus “pops out” from the rest

* RT does not depend on display size (or is dependent to a much lesser degree)

feature-based recognition

damage to the parietal cortex results in difficulty in judging how more than one feature is bound together in objects

* integrative agnosia
* disruption of parietal cortex via TMS
* subject can do a feature search but not a conjunctive search

Word frequency effect

high frequency words recognized better

Repetition priming effect

recently viewed words recognized better

Word superiority effect

letters recognized better in the context of a word

* response when asked whether “DARK” has an “E” or a “K” is more accurate than when “E” or “K” is presented alone
* effect does not occur if a letter string such as “JPERW” is used instead of a real word

Feature nets

propose that recognition depends on a network of “detectors”, organized in layers of increasing granularity

* "Neural networks”
* have receptive fields
* fire above threshold
* detectors do not represent actual individual neurons
* recent firing = higher starting activation level
* explains word frequency effect and repetition priming

bigrams

a pair of consecutive written units such as letters, syllables, or words

* can be part of the neural network
* helps explain the word-superiority effect

Ventral stream

the **what** pathway

* refers to the visual paths in the temporal cortex
* specialized for identifying and recognizing objects

Dorsal stream

the **where** pathway

* refers to the visual path in the parietal cortex
* helps the motor system to find objects and move towards them

Single dissociation

one function is lost, another remains

* ie: one stream is damaged but not the other
* shows that the what and where rely on different mechanisms, although they may not operate totally independent of one another

Double dissociation

requires two individuals with different damage and opposite deficits

* indicates that the what and where streams must have different mechanisms and operate independently of one another

Visual agnosia

the inability to recognize objects despite satisfactory vision

* there are many types of visual agnosia, caused by damage to various visual areas (occipital, temporal, or parietal)
* can identify people and faces
* their knowledge is accessible to other pathways (ie: touch), but not their visual pathway

Prosopagnosia

is a type of agnosia also know as face blindness

* occurs after damage to the fusiform gyrus of the inferior temporal cortex
* can see the textures and features of a face but cannot put them together to recognize or identity the face

Holistic processing

we process faces as a whole

* harder to process just the top or just the bottom when the faces are aligned