Sensation & Perception

What is attention?

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

Overt attention

attention that involves looking directly at the attended object

Covert attention

looking at one object but attending to another object

Saccades

quick eye movements from one fixation point to another

What directs our attention?

- An initial involuntary process mediated by attentional capture

- A voluntary process (guided by your goals and expectations)

Attentional capture

Determined by salience

What Captures Our Attention?

- Regions of colour contrast or luminance contrast

- Regions of size contrast

- Regions orientation contrast

- Regions of motion/flicker contrast

Syntactically inconsistent object

an object that belongs in a scene but something is not right

Semantically inconsistent object

an object that doesn't belong in the scene

What Are the Effects of Attention?

Attention speeds responses, influence appearances, influence physiological responding

The Binding Problem

how features are linked together so that we see unified objects in our visual world rather than free-floating or miscombined features

Feature Integration Theory

features associated with one location are processed, so only those features are bound together

Illusory Conjunctions

combinations of features from different objects

Balint's Syndrome

inability to focus on a single object --> illusory conjunctions

conjunction search

search for a target defined by the presence of two or more features

feature search

search for a target defined by a single attribute, such as a salient color or orientation

Change blindness

failing to notice changes in the environment

factors that make perception hard

- The stimulus on the retina is ambiguous

- Objects can be hidden or blurred

- Objects look different from different viewpoints and in different poses

Structuralism

Edward Titchener - distinguishes between sensations and perceptions

Gestaltism

Apparent motion

Illusory contours

Perceptual organisation

grouping and segregation

Gestalt Principles of Grouping

continuation, praganz, proximity, similarity, proximity, common fate, common region, uniform connectedness

Figural Properties

They are in front of the rest of the image, at the bottom, convex, recognisable

Gist Perception

Quick understanding of a scene's overall meaning.

what can motion perception help do?

Camouflage, attract attention, segregate objects from the background, interpret events, determine the structure of objects, determine what actions people are performing

akinetopsia

inability to see objects in motion

consequences of akinetopsia

Difficulties pouring a cup of tea, Crossing the street, Following speech

When Do We Perceive Motion

real motion, illusory motion, motion aftereffects, induced motion

Kitaoka & Ashida, 2003

Rotating Snake Illusion

Korte's Third Law of Apparent Motion

as separation increases alternation rate needs to decrease

Robert Adams

the waterfall illusion

Induced Motion

The illusory movement of one object that is caused by the movement of another object that is nearby.

Motion induced blindness

motion can make salient objects disappear

Suchow & Alvarez (2011)

Moving dots experiment

Motion Illusions

Footsteps illusion, Barber Pole Illusion

aperture problem

The fact that when a moving object is viewed through an aperture (or a receptive field), the direction of motion of a local feature or part of the object may be ambiguous.

What can colour perception help

Find things (like berries, Determine if fruit is ripe, Spot (and identify) poisonous animals, identify a potential mate

What is the wavelength on electromagnetic radiation (visible light)

400 - 700 nm

What is the colour of an opaque object determined by

The light that it reflects

What is a transparent object determined by

the colour it transmits

Yellow paint

absorbs blue light, reflects red and green light

Blue paint

Absorbs red light, reflects blue and green light

short (S)wavelength light

Blue

Medium wavelenght light

green

long wavelength light

red

White light

mix of all three colours

Munsell Colour System

value, hue, chroma

Trichromatic Theory of Vision

rods and cones (photoreceptors) in the retina

How many types of cones are there?

3 (red, green, blue)

How are humans able to distinguish between colours

comparing the relative activities of these threetypes of cones

Two main types of colour deficiency

Monochromatism Dichromatism

metamers

two lights that have different wavelength distributions but are perceptually identical

Monochromatism

the inability to see colours

Dichromatism

Missing 1 cone

Protanopes

lack of L red cones

- cant distinguish red/green

Deuteranopia

lack of M green cones - cant distinguish red/green, see the world in shades of blue and a yellowish-green

Tritanopia

lack of S blue cones

-cant distinguish blue and green, see the world in shades of blue and red

Opponent-Process Theory of Colour Vision

The hypothesis that colour vision is based on three pairs of opponent channels.

Afterimages

Opposite colour that linger after the stimulus is removed

Is a reddish green possible?

No as they are opponent colours

What is the afterimage of yellow?

blue

What is the afterimage of red

green

Colour Constancy

colour of light an object reflects is also determined by the colour of light shining on it

What does reflected light incorporate

Reflectance x Illumination = Reflected light

Why do we continue to see green even under predominantly red light?

Habituation,Discounting the Illuminant

Perceiving Depth

Oculomotor cues, Monocular cues, Binocular cues

Oculomotor Cues

Binocular Convergence, Accommodation (lens thickening)

Monocular cues

Accommodation, Pictorial cues, Movement-based cues

Pictorial Cues

- Occlusion

- Relative height

- Familiar and relative size

-Perspective convergence

-Atmospheric perspective

-Texture gradient

- Shadows

Movement-Based Cues

- Motion parallax - closer things move slower

- Deletion and accretion - objects moving behind others

Binocular cues

Binocular Disparity, Relative Disparity, Absolute Disparity

Binocular disparity

slightly different view of the world that each eye receives

Relative Disparity

The difference between two objects' absolute disparities.

Correspondence Problem

In binocular vision, the problem of figuring out which bit of the image in the left eye should be matched with which bit in the right eye

Perceiving Size

- angular size

- perceived depth

Size Constancy

an object's apparent size does not depend on is physical distance

Formula for size constancy

S = K x (R x D)

Where S = apparent size of an object

K is a constant

R = size of the retinal image

D = perceived distance to the object

Ames Room

a distorted room that is used to create an optical illusion

Holway and Boring (1941)

participants adjusted size of comparison circle ten feet away to match size of test circle at constant visual angle but variable size and distance; when there are sufficient depth cues, the size of the test patch can be accurately estimated. When there are not sufficient depth cues, the apparent size of the test patch is biased towards the visual angle

sound

physical phenomenon (e.g. sound waves and pressure changes) and to the perceptual phenomenon (sensation)

What speed do pressure waves move through the air

340 m/s

Pure Tones

sounds with a single frequency wave

Human range of hearing

20-20,000 Hz

The greater the amplitude...

the louder the sound seems

db of a hairdryer

70

db of a susbway

100

db of Jet plane takeoff

120

db of a Gunshot

130

complex tones

sounds with a mixture of frequencies

Fundamental frequency

first harmonic - the lowest frequency of vibration of a standing wave

What is perceptually loudness measured in

phons

Pure tone - Pitch

determined by frequency

Complex tone - Pitch

usually determined by the fundamental frequency

How to describe pitch

in terms of musical notes

what is c1 and c2 seperated by on a keyboard

an onctave

Chroma

similar sound shared by notes of the same letter

Tone height increases when

moving left to right on the keyboard

Missing Fundamental

the complex tone will continue to repeat at the fundamental frequency, even when the fundamental frequency is absent

Timbre

Different instruments play different harmonics - the same note will sound different

Tuning fork + flute

not many repetitions of the fundamental frequency