sensation & perception

Question 1

sensation

Answer 1

the activation of receptors in the various sense organs. Gathering info from your senses

Question 2

perception

Answer 2

organization, identification, & interpretation of sensory info in order to represent & comprehend the environment (external & internal )

Question 3

Early visual processing - bottom up process

Answer 3

Info from the physical stimulus is used to help recognize a stimulus
Start with small bits of info & combine them to form your perceptions
Stimulus constrained

Question 4

Late visual processing- top down process

Answer 4

Previous knowledge is used to help recognize a stimulus
High level general knowledge contributes to the interpretation of the low-level perceptual units
Context constrained
Top down approach needed to make sense of our perceptions
Sharing our experiences (perceptions) require similar top-down processing

Question 5

Evidence of topographic organization

Tootel, Silverman, Switkes, & De Valois (1982)

Answer 5

A visual stimulus is presented to a monkey

Monkey is given qualities of radioactive sugar what is taking up by the more active cells in the cortex

Looking at an x ray picture of the cortex they can see what cell were the more responsive to the pictures

Shows a relatively precise mapping: ajacent areas in the visual cortex represent info from adjacent areas of the visual field

Question 6

Polimeni, Fischl, Greve & Wald (2010)

Answer 6

With humans using a 7 tesla fMRI

Question 7

Early visual processing (Edge detectors)

Answer 7

Ganglion cells fire at some spontaneous rate even when the eyes are not receiving any light

On-off cells: responds positively to light in the center (rate increase) & negatively to light at the periphery (rate decreases)

Off-on cells: responds negatively to light in the center (rate decreases) & positively to light at the periphery (rate increases)

Examples:
Mach band illusion
Hermann Grid illusion

Question 8

Early visual processing (light & color)

Answer 8

Rod cells
Very sensitive to low light (but no color)
Respond very fast (motion) 
Concentrated in the peripheral retina 
Approx 100 million per eye 

Cone cells
Not sensitive to low light
Respond slowly & require more light to function
3 types which respond differently to light of varying wavelengths, providing us with color vision: L cones for “red”, M cones for “green” & S cones for “blue”
Concentration in & near the fovea

Question 9

Perceiving depth

Answer 9

Texture gradient
Elements tend to appear more closely packed together as the distance from the view increases

Stereopsis
The fact that two eyes receive slightly different view of the world

Motion parallax
More distant points will move more slowly across the retina than closer points

Question 10

Visual info processing

Visual pattern recognition

Answer 10

Template- matching models
Feature analysis
Recognition- by- components theory

Question 11

Template-matching models

Answer 11

A retinal image of an object is faithfully transmitted to the brain

An attempt is made to compare it directly to various stored patterns (templates)

Question 12

Feature analysis

Answer 12

Stimuli are thought of as combinations of elemental features

We can perceive an object because what we store in our long-term memory are its parts/ features

We compare retinal image & see what object in long-term memory has most features that match the object
Pritchard (1961)

Features are the important units in perception

These features are combined to define the recognized patterns

Question 13

Recognition by components theory

Answer 13

Recognition of complex objects the defy description in terms of a few features

Biederman proposes 3 substages:

1. The object is segmented into a set of basic subojects
2. Classification of each suboject into a category (geons)
3. Recognition of the object as the pattern composed from these pieces (geons)

Question 14

The Thatcher Effect

Answer 14

It is difficult to detect local feature changes in an upside down face, despite identical changes being obvious in an upright face

Holistic (faces) vs features base processing

Question 15

Gestalt Principals of Perceptual Organization

Answer 15

We perceive complex scenes as composed of many groups of objects on some background, with the objects themselves consisting of parts, which may be composed of smaller parts, etc

Gestalt principals of perceptual organization: rules of the organization of perceptual scenes

–They aim to formulate the regularities according to which the perceptual input is organized into a whole form

–These principles will tend to organize even completely novel stimuli into units

Question 16

principals

Answer 16

Principal of proximity: Elements close together tend to organize into units
Principle of similarity: objects that look alike tend to be grouped together
Principle of of good continuation: lines or curves that follow an established direction tend to be grouped & organized together
Principle of closure & good form: forms of similar shape, form, color, pattern & other attributes tend to be perceived in group. If there is a break in the object, we perceive the object as continuing a smooth pattern

Question 17

Preceiving Constancies

Answer 17

Sensory messages are unstable, always changing, yet we need to perceive a stable world

Color constancy: ensures that the perceived color of objects remains relatively constant under varying illumination conditions

Size constancy: images change with distance, but size stays the same

Shape constancy: images change with motion, perspective, but shape seems to stay the same

Example:
Muller- Lyer Illusion:
ponzo illusion:
The Ames room: