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1

What is the Perceptual Process ?

The perceptual process begin with stimuli in the environment and ends with the behavioral responses of

- perceiving
- recognizing
- taking action

2

Principle of Transformation

Stimuli and the responses created by stimuli are transformed between environmental stimulus and perception

3

Eye's optical system

- consists of the cornea + lens

--> they form a sharp picture of the stimulus on the receptors of the retina

4

Principle of representation

Everything a person perceives is based on representations of stimuli that are formed on the receptors and the activity in the persons NS

5

What are sensory receptors ?

Cells specialized to respond to environmental energy with each sensory systems receptors specialized to respond to a specific type of energy

ex.: visual receptors - light, auditory receptors - pressure changes in air

6

Function of Visual receptors

1. Transforming environmental energy into electrical energy (Transduction)

2. Shaping perception by the way they respond to stimuli

7

Transduction

Transformation of one form of energy to another form

8

Visual pigment

Light sensitive chemical that reacts to light

- found in visual receptors

- transforms light into electrical energy

- without it perception wouldn't occur because the information about the representation of the stimulus in the retina wouldn't reach the brain

9

Function of the network of neurons

1. Transmits signals from receptors (retina) to the brain

2. Changes these signals because there are multiple routes with signals

a) traveling in the opposite directions
b) being amplified
c) being reduced or prevented from entering

10

Primary receiving area

Receives signals from each sense

--> located in the cerebral cortex

11

Which lobe can you assign to which sense ?

Occipital lobe --> vision

Temporal lobe --> hearing

Parietal lobe --> touch

Frontal lobe --> all senses, plays important role in coordination of information received from 2 or more senses

12

Perception

Conscious awareness of the stimulus (active)

--> top down processing

13

Recognition

Placing an object in a category, that gives it meaning

14

Visual form of agnosia

Inability to recognize objects /

Perceiving parts of the object, but not being able to identify the whole object

15

Action

Refers to the mere act of looking at different parts of the stimulus, no need to interact with it

--> usually involves motor activities

16

Knowledge

Any information the perceiver brings to a situation

--> can affect a number of steps in the perceptual process
--> can be recently acquired information or acquired years ago

17

Bottom up processing

Processing, that is based on stimuli reaching the receptors

--> 'incoming data'

18

Top down processing

Processing based on knowledge (Schemas)

19

Psychophysical approach/
Psychophysics

Measures the relationship between the stimuli and behavioral response

--> presenting a stimulus and determining the persons response

20

Oblique effect

There is a better detail vision for vertical and horizontal lines than slanted lines

21

Physiological approach

Measures the relationship between

1. Physiological responses + stimuli

2. Physiological responses + behavioral responses

--> used to understand the physiology behind the oblique effect

22

Absolute threshold

Describes the minimum stimulus intensity that can just be detected

ex.: Vision --> the smallest line that can barely be seen

--> threshold is lower (finer lines can be seen) when the lines are horizontal/vertical

23

Human perception is variable.
How can this affect measurements ?

Measurements at one point in time can differ slightly from measurements at another point.

24

Method of limits
(Classical psychophysical method)

Fechner

Experimenter presents stimuli by either ascending or descending order

--> threshold is the average of all crossover points
--> increasing or decreasing intensity

25

Crossoverpoint

The change/ Point when the observer goes from perceiving the stimulus to not perceiving it anymore or vice versa

ex.: hearing a sound --> not hearing it anymore

--> may vary slightly, procedure is therefore repeated

26

Method of adjustment
(Classical psychophysical method)

Fechner

Observer increases/decreases stimulus intensity until the stimulus can just be detected

--> fastest method because the observers can just adjust their threshold quickly

27

Method of constant stimuli
(Classical psychophysical method)

Fechner

Experimenter presents 5 to 9 stimuli with different intensities in a random order

--> threshold is the intensity that results in detection on 50% of the trials

--> most accurate method, but time consuming

28

Difference threshold

Describes the minimum difference that must exist between 2 stimuli before we can tell the difference between them

--> Differenze Limen (DL)

29

Weber fraction

The ratio of DL vs Standard always corresponds to a certain percentage

ex.: weight = 0.02

--> each type of sensory judgment has its own weber fraction

30

Weber law

The weber fraction remains the same as the standard is changed

ex.: if the weight is doubled, DL is doubled too