MBB1 - SENSATION AND PERCEPTION

ATTENTION

the ability to preferentially process some part of a simulus at the expense of processing of other parts of the stimulus

OVERT ATTENTION

looking directly at an object

COVERT ATTENTION

looking at one object but attending to another object

FIXATION

where your eyes are looking, the rest between saccades

SACCADE

ballistic eye movements between fixations

ATTENTIONAL CAPTURE

• intial involuntary process

• when a scene is first presented, fixations are captured by the salient part of the scene

• forgoes goals and expectations of the viewer

SALIENCE

the quality of being noticeable

SEMANTICALLY CONSISTENT OBJECT

the sort of object you would expect to see in a specific place

SEMANTICALLY INCONSISTENT OBJECT

an object in a scene that is unexpected

MORE SALIENT

SYNTACTICALLY INCONSISTENT OBJECT

an object you would expect to find in a space, but in an unexpected position

WHAT DIRECTS OUR ATTENTION?

• initially fixations are involuntary (attentional capture)

• then, fixations are voluntary, goal directed and influenced by our expectations

EFFECTS OF ATTENTION

• speeds responses

• influence appearance

• influence physiological responding

• can affect the physiological response to a stimulus

THE BINDING PROBLEM

• different aspects of stimuli are processed in different areas of the brain (ie colour and movement)

• these processes need to be BOUND to form a coherent perception

• why do we not see a coloured object and a moving object as different objects?

• why can we differentiate multiple objects

FEATURE INTERGRATION THEORY (FIT)

• suggests the BINDING PROBLEM is solved by attending to only one location at a time

• we only process features associated with a specific location, only attending to one object at a time

ILLUSORY CONJUNCTIONS

• according to FIT if attention is inhibited, features of different objects will be combined

BALINT’S SYNDROME

• caused by damage to the parietal lobe

• when multiple objects are presented, the viewer has difficulty focusing attention on a single object

• prone to experiencing illusionary conjunctions

VISUAL SEARCHES

looking for objects

• conjunction searches and feature searches

CONJUNCTION SEARCHES

• EG looking for a RED and HORIZONTAL line (target) in a group with other objects with similar features (distractors)

• require the binding problem to be solves

• slow

FEATURE SEARCHES

• EG looking for RED object in a group of green objects

• don’t require the binding problem to be solved

• fast

CHANGE BLINDNESS

• if you dont attend you won’t remember

• you can only remember a few parts of a scene at a time, if they change, you notice

• if other parts of the scene change, you likely won’t notice

THE GORILLA DRUMMING THING

MOTION TRANSIENTS

• generated by change in an image, drawing attention and making us notice the change

• STOPS CHANGE BLINDNESS

WHAT MAKES OBJECT PERCEPTION SO HARD?

• the stimulus on the retina is ambiguous

  • different shaped objects form the same image on the retina

• objects can be hidden or blurred

• objects look different from different perspectives

HOW ARE HUMANS SO GOOD AT PERCEPTION?

• structrualism

• gestaltism

STRUCTURALISM

• distinguishes between sensations and perceptions

• claims that sensations combine to form perceptions

• perceptions contain nothing that was not present in the sensations

SENSATIONS

• elementary processes occurring in response to stimulation

PERCEPTIONS

• conscious awareness of objects and scenes

GESTALTISM

• contradicts structuralism

• claims perceptions are not entirely made of sensations

• IE they can contain elements not present in sensations

EVIDENCED BY:

• apparent motion

• illusory contours

APPARENT MOTION

• observer sees two STATIONARY dots flashed, and perceives ONE MOVING DOT

• ie the conscious percept of motion was constructed even though it was not present in sensation

ILLUSORY CONTOURS

• seen where there are no contours

PERCEPTUAL ORGANISATION

the ability to distinguish between objects

EG a person sitting on a chair, i can see where the person is and where the chair is

• achieved through GROUPING and SEGREGATION

ALLOWS OBSERVERS TO MAKE SENSE OF A SCENE

GROUPING

parts of an image are perceptually bound together to form a perceptual whole (the perception of an object)

SEGREGATION

parts of a scene are perpetually seperated to form seperate wholes (the perception of separate objects)

GESTALT PRINCIPLES OF GROUPING

• good continuation

• pragnanz

• similarity

• proximity

• common fate

two more (added later)

• common region

• uniform connectedness

GOOD CONTINUATION

• aligned contours are grouped together to form a single object

• if i put 2 ropes in a cross, I would be able to tell which is which

PRAGNANZ

• german for good figure

• groupings occur to make the figure as simple as possible

SIMILARITY

the more similar objects are the more likely they will be grouped

PROXIMITY

the closer objects are the more likely they will be grouped together

COMMON FATE

objects that move in the same way (two dots moving left vs two dots moving right) will be grouped

stronger than proximity

COMMON REGION

elements within the same region of space tend to be grouped together

UNIFORM CONNECTEDNESS

connected regions with the same visual characteristics (eg colour) tend to be grouped together

GESTALT PRINCIPLES OF SEGREGATION

• typically determined by distinguishing figure and ground

FIGURAL PROPERTIES

how we determine what is figure in a scene

objects are more likely to be seen as figure if:

• they are in front of the rest of the image

• they are at the bottom of an image

• they are convex

• they are recognisable (ie overlapping letters are distinguishable)

GIST PERCEPTION

when an object is flashed quickly you may not be able to remember every detail, but you’re able to gain a general GIST of what the scene contains

this is an overall impression

• 27 MS is enough to extract some gist

• 250 MS is enough to achieve a detailed perception

MOTION PERCEPTION

helps with

• breaking camoflage

• attract attention

• segregate objects from the background

• interpret events (conveying social relationship)

• determine structure

• determine what actions people are performing

AKINETOPSIA

a condition in which the person is unable to percieve motion

caused by damage to the dorsal pathway

• patients can see that things had moved but could not see them moving

REAL MOTION

an object is actually moving

ILLUSORY MOTION

nothing is moving but it looks like it is, eg static image, apparent motion

MOTION AFTEREFFECTS

occurs after watching an object move for a long time, when the objects around it appear to move in the opposite direction

INDUCED MOTION

Moving background (or a moving object) causes a stationary object to appear to move

MOTION INDUCED BLINDNESS

motion can make things disappear

MOTION INDUCED CHANGE BLINDNESS

when objects are moving it is difficult to perceive changing colours

this is due to an excess of motion transients

APERTURE PROBLEM

if you can’t see the ends of a line, the movement of a line is ambiguous, thus the line appears to move in a different direction than in reality

MOTION ILLUSIONS

• footsteps illusion

• barber poll illusion

FOOTSTEPS ILLUSION

the contrast of the two rectangles changes as they slide across the black and white bars, making them appear to speed up and slow down

BARBER POLL ILLUSION

caused by the aperture effect, when the ends of the lines are obscured, they appear to move in a different direction than they do in reality (ie moving up and down, when really they are just spinning)

FUNCTIONS OF COLOUR PERCEPTION

• identifying threats (poisonous animals are often coloured)

• identifying foods

• identify potential mates

PHYSICS OF COLOUR

visible light is electromagnetic radiation

wavelengths vary from 400nm to 700nm

white light is a mixture of all wavelengths

COLOUR OF OPAQUE OBJECTS

an object that light cannot pass through

its colour is determined by the light it reflects

(if it absorbs blue, but reflects red, it looks red)

COLOUR OF TRANSPARENT OBJECTS

determined by the colour it transmits

(if it absorbs blue, but transmits red, it looks red)

MUNSELL COLOUR SYSTEM

value = light

hue = colour

chroma = saturation

TRICHROMATIC THEORY OF VISION

by comparing the relative activity of the 3 types of cones, we are able to determine what colour we are looking at

RODS

only active at low light levels, cannot distinguish between colours

at normal light levels, they become oversaturated

CONES

there are 3 types of cones, they respond to different extents to different wavelengths

• S cones – 419 nm (blue)

• M cones – 531 nm (green)

• L cones – 558 nm (red)

its response is determined by the wavelength and by the intensity of the light

COLOUR MATCHING

if you have a light thats a colour, and you replicate that light by combining lights of different colours, the ‘match patch, will appear the same to your eye even if its objectively not

different stimuli that appear the same are called METAMERS

MONOCHROMATISM

• colour deficency

• usually have no functioning cones, only rods

• see the world only in shades of grey

DICHROMATISM

• lacking one of the three cone types

• THREE TYPES INCLUDE

  • protanopes

  • deuteranopes

  • tritanopes

• for them, it is possible to colour match with only 2 sets of lights

PROTANOPES

lack L cones (blue)

cant distinguish between red and green

DEUTERANOPES

lack M cones (green)

cant distinguish between red and green

TRITANOPES

lack S cones (red)

can’t distinguish between blue and green

UNILATERAL DICHROMATS

dichromats only lacking a cone type in ONE EYE

OPPONENT-PROCESS THEORY OF COLOUR VISION

• signals from cones are processed by the cortex and combined into three colour opponent channels

  • red-green

  • blue-yellow

  • white-black

• psychophysical evidence for this theory:

  • afterimages

  • impossible colours

AFTERIMAGES

if you stare at something RED, then you see white, you will see something GREEN

if you stare at something YELLOW (made of green+red), then you see white, you will see something BLUE

this is because the different cone types have been habituated

IMPOSSIBLE COLOURS

it is possible to see blueish-red (purple) and yellowish-red (orange) but it is not possible to see a greenish-red or a yellowish-blue because these colours are OPPOSING

(adding these colours together create white and yellow respectively)

COLOUR CONSTANCY

• the colour of light an object reflects is determined by not only the reflectance, but also the COLOUR OF LIGHT SHINING ON IT

• REFLECTANCE X ILLUMINATION = REFLECTED LIGHT

• how do we still see green even under red light? we HABITUATE (become less sensitive to red light if everything is under red light)

DISCOUNTING THE ILLUMINANT

sometimes habituation cannot occur because there is a the same amount of blue and yellow

IE: if the patch is illuminating grey under a yellow light, it must be blue! says our eyeballs

EG THE BLUE AND BLACK DRESS, there were not enough visual cues in the image so different people were discounting different illuminates

PERCIEVING DEPTH

requires 3 different kinds of cues

• oculomotor cues

• monocular cues

• binocular cues

OCULOMOTOR CUES

cues based on our ability to sense the position and state of our eyes

INCLUDES:

• binocular convergence

• accomodation

BINOCULAR CONVERGENCE

when the sightlines of your eyes converge to look at something closer to you

ACCOMODATION

the changing of the width of the lens in your eye, based on the distance of the focal point

MONOCULAR CUES

cues based on the visual information available with one eye

• accomodation

• pictorial cues

• movement based cues

PICTORIAL CUES

include:

• occlusion (whats behind what)

• relative height (things look lower down when they are further away)

• familiar and relative size (things look smaller when they are further away)

• perspective convergence (parallel lines converge when points are further away)

• atmospheric convergence (things are blurrier when theyre further away)

• texture gradient (you see more texture when things are closer)

• shadows (estimate the height of the object above a background)

MOVEMENT BASED CUES

monocular cues

include:

• motion parallax

• deletion and accretion

MOTION PARALLAX

closer objects move faster relative to you

DELETION AND ACCRETION

relative to your movement, objects are obscured (deleted) and accreted from behind other objects

allows you to gauge depth ordering

BINOCULAR CUES

cues that depend on visual information within both eyes

DISPARITY

the difference in images between the left and right eyes

the position of the image in the left eye MINUS the position of the image in the right eye

BINOCULAR DISPARITY

because there is distance between your eyes, they perceive the world from slightly different viewpoints’

fixated images occur in the same position on both retinas

objects BEHIND the fixated image occur on opposing sides of the retina in each eye (NEGATIVE DISPARITY)

objects IN FRONT of the fixated image also occur on opposing sides of the retina in each eye (POSITIVE DISPARITY)

NEGATIVE/CROSSED DISPARITY

objects BEHIND the fixated image occur on opposing sides of the retina in each eye

(between the fixated image)

POSITIVE/UNCROSSED DISPARITY

objects IN FRONT of the fixated image also occur on opposing sides of the retina in each eye

(outside the fixated image)

HOROPTER

the line in which all objects will fall on the corresponding part of the retina in both eyes even if they are not the point of fixation

CORRESPONDENCE PROBLEM

If there are multiple identical objects in the scene it can be hard to figure out which images in the left retinal image should be associated with which images in the right retinal image

BASICALLY how do you tell depth when these two scenes make the same image on the retina?

THE RETINAL IMAGES ARE IMBIGUOUS unless the objects are coloured

PERCEIVING SIZE

perceived size is determined by:

• angular size

• its perceived depth

ANGULAR SIZE

the visual angle of the object on the retina

SIZE CONSTANCY

phenomenon where an objects apparent size does not depend on its physical distance

(ie i can see that a far chair is smaller than a near chair, but i know that they are relatively the same size)

this is achieved by considering the size of the object on the retina and the distance of the object

S(size) = K(constant) x (R[size of retinal image] x D[perceived distance of object])

S = K x (R x D)

SIZE ILLUSIONS

caused by people mistaking the distance of an object, making it appear larger or smaller than reality

AMES ROOM

optical illusion in which a person in one corner appears much smaller than a person in the other corner

PHYSICAL DEFINITION OF SOUND

pressure changes in the air or other medium

PERCEPTUAL DEFINITION OF SOUND

the experience or sensation we have when we hear

PURE TONES

occurs when the change in air pressure occur in a SINE WAVE

• the higher the frequency the higher the pitch

FREQUENCY

how frequent the sound waves are

measured in Hz

(200 Hz = wave repeats 200 times a second)