Human Perception Exam 2

retina circuitry

sensitivity and resolution.

many-to-one convergence

promotes sensitivity.

one-to-one convergence

promotes spatial resolution.

overview of visual processing

light enters the eye —> retina converts light into signals —> signals travel to brain —> brain interprets the image —> ability to see!

excitatory-center, inhibitory-surround RF

on-center ganglion cell.

inhibitory-center, excitatory-surround RF

off-center ganglion cell.

function of the center-surround receptive field

detecting a spot of light and detecting a edge of a stimulus.

parasol ganglion cell

magno-cellular pathway.

• color blind.

• FAST (temporal frequency).

• HIGH contrast sensitivity.

• LOW spatial resolution.

midget ganglion cell

parvo-cellular pathway.

• color selective.

• SLOW (temporal frequency).

• LOW contrast sensitivity.

  • HIGH spatial resolution.

retinotopy

mapping of visual input of the retina neurons, particularly those neurons within the visual stream.

cortical magnification

foveal area is about 0.01% of whole retina, but signals from the fovea account for 8 to 10% of the retinotopic map on the cortex.

orientation selectivity

orientation tuning of a “simple cell” in V1.

• we need an elongated receptive field.

cortical organization

columnar structure for orientation and ocular dominance.

selective adaption technique

when we view a stimulus with a specific property, neurons tuned to that property fire, and if viewing continues for long enough, these neurons adapt.

effects of adaption

1. decrease in firing rate of the adapted neuron.

   1. decrease in sensitivity when the adapting stimulus is immediately presented again.

selective adaption to orientation

researchers test orientation adaptation by first measuring a person’s sensitivity to various line angles. After the person stares at a line tilted in one direction for one to two minutes, their sensitivity is measured again. If adaptation occurs, sensitivity to the viewed orientation should decrease, while sensitivity to other angles remains unchanged.

ventral and dorsal streams

“what” and “where” pathways.

object discrimination problem

object recognition.

landmark discrimination problem

relative location.

“where” pathway

integrating with an object involves knowing the location of the object.

“how” pathway

dorsal stream involves in how to direct actions for interacting with objects in environments.

neuropsychological study showing how-pathway

behavior of patient D.F.

single dissociation

cannot make an orientation match, but can put a card into an oriented slit.

double dissociation

a patient whose symptoms are exactly the opposite to D.F. can be founded.

modularity

the structures located along the ventral and dorsal pathways are often specialized to process information about specific visual qualities.

fundamental spatial information

• orientation

• contrast

• spatial frequency

• spatial phase

spatial frquency

building blocks of visual images.

gestalt approach

perception is created by combining elements called sensation.
(this doesn’t explain several perceptual phenomena such as Apparent Motion and Illusory Contour).

the whole differs from the sum of its parts

perception is not just created by combining elements, perceptual organization creates a “whole” from small parts.

properties of figure and ground

• figure is object-like and in front of the ground.

• ground is uniform region behind the figure.

• both share a contour (boarder ownership).

heurisitics

rules of thumb that provide a best-guess solution to a problem.

algorithm

a procedure that is guaranteed to solve a problem.

likelihood

we perceive the object that is most likely to have cause the pattern of stimuli.

why is visual recognition hard?

difference sizes, 2D orientation, 3D views, and exemplars.

inverse projection problem

different objects can give rise to the same retinal image.

template model

simple and intuitive, but lacks flexibility.

some limits are the massive number of templates are required.

a possible solution is the Feature-Based Model.

feature-based models

fixed set of elementary properties analyzed independently in parallel across visual field.

a limit is different objects share the same features and relationships.

recognition by component theory

objects are represented by a small set of geons and their relationships.

configural and holistic face processing

better at recognizing a face part (i.e. nose) if presented in context of a face (holistic).

specialized modules (nancy kanwisher)

specialized bran areas for processing certain stimuli: face, places, bodies (sparse coding).di

distributed representations (jim haxby)

faces and objects represented by distributed patterns of activity in ventral temporal cortex.

expertise (isabel gauthier)

fusiform area important for expert processing: subordinate-level recognition, not face recognition.

fusiform face area (FFA)

module specialized for faces since it responds more to faces than to:

• common objects.

• scrambled faces.

• houses.

• hands.

• flowers.

distributed representations theory

Design: subjects viewed 1 of 8
categories of stimuli.

Results: activity patterns in
ventral temporal cortex
measured from first 1/2 of EXP
could accurately predict what
object category was seen in
2nd half of EXP 96% accuracy
(chance 50%).

cognitive resources

a person has a certain cognitive capacity, which can be used for carrying out various tasks.

cognitive load

the amount of a person’s cognitive resources needed to carry out a particular cognitive task.

multiple object tracking

people (even 5yo children, though not most professors) can track 4 to 5 individual objects that have no unique visual properties.

broadbent (1958)

attention works like a bottleneck of information processing stream.

late selection theory

selection occurs at the late stage of information processing (the bottleneck located later in the processing, after meanings of the messages have been extracted).

divided attention

can be achieved with practice.

automatic processing

can be achieved if the relationship between target and distractors keeps changing.

controlled processing

need a lot of cognitive resources.

covert attention

without eye movement.

spotlight metaphor

cover only small spatial region, fuzzy boundary.

location-based attention

visual attention is directed to a particular location in the visual scene.

posner (1980)

spatial cueing; target detection is faster and more accurate with valid cue.

object-based attention

visual attention is directed to objects or perceptual groups of visual scene previously segmented on the basis of gestalt principles.

balint’s syndrome

cause: bilateral parietal damage.

effect: patient can only perceive one object at a time.

feature integration theory

focused attention have a major role for binding features to achieve a representation of an object.