Sensation and Perception

Change Blindness

inability to notice changes to visual scene which in retrospect seems obvious

Attention

concentration of mental effort on sensory or mental event

Selective Attention

Focusing on Specific information while ignoring other distractions

Divided Attention

Attempting to process multiple sources of information simultaneously

inattention blindness

Failing to notice fully visible, unexpected object when attention is engaged on another task - attention is necessary for conscious perception

Attention spotlight

mental spotlight that can be moved around the field of vision, highlighting objects for detailed process

• limited scope

• can be shifted

• information within the spotlight is processed more effectively

Salience

objects that stand out and readily draw attention

The blinding problem

challenges how the brain combines an object’s individual features which are often processed independently in seperate brain areas to create a single coherent perception of that object

Illusory Conjunctions

error in binding where features of an object are incorrectly combined resulting in a a perceived object that does not exist in reality.

Feature integration theory

Explains how we perceive objects as a unified whole by proposing two stages of processing

1. Pre-attentive stage - feature are processed automatically, rapidly and in parallel across the visual field, attention is not required

2. Focused Attention Stage - Attention is serially directed to specific locations, glue features together at that location to create coherent object

Feature Search

If target can be identified by single unique feature, it will stand out and be processed i the pre-attentive stage. search time is fast and largely independent of the number of distractors

Conjunction Search

If target is defined by a combination of features, attention is required to bind features. search is slower and serial, increasing the number of distraction also slows process further

Geons - geometric ions

proposes that objects are recognised by decomposing them into basic 3d shapes called geons

View dependant theories

proposes that objects are recognised by comparing incoming visual input to multiple stored views of the object. Recognition is easier when the object is seen from a familiar view point

Motion Perception

provides crucial information about objects, and helps to navigate the enviornment

Motion is processed primarily in the middle temporal area(V5)

Real Motion

Physical movement of an object from one position to another

Apparent Movement

Perception of motion created y static images presented sequentially with breif intervals

Induced motion

Occurs when stationary object appears to be moving due to movement of surrounding background or frame

Motion aftereffects

When you view motion in one direction for too long, and then look at a stationary object, will then appear to be moving in the opposite direction

Retinal image vs head/eye movement

distinguishes movement between object movement and movement of your head and eyes

• Image-retina system - detects changes in retinal image as object moves across the retina, this system is active when your eyes are stationary and an object moves

• Eye head system - Accounts for motion generated by our own movements

Aperture problem

individual motion-sensitive neurons that can only see a small portion of the visual field through their receptive field. when moving line or object is viewed through small aperture, the perceived direction of motion is ambiguous because the the end line are not visible.

a single neuron cannot determine the entire objects true direction

is solved by integrating information from multiple motion sensitive neurons with different receptive fields

Trichromatic theory of colour vision

Proposes that colour vision is based on the activity of three different types of cone photoreceptors in the retina, each maximally sensitive to a different range of wavelengths

short cones - most sensitive to blue

Medium cones - most sensitive to green

Long cones - most sensitive to red

colour perception is determined by the ratio of activity across these three cone types

supported by colour matching(Mixing primary colours) and colour deficiency(colour blindness)

limitations - afterimages, complementary colours

is the initial processing

Opponent process theory of colour

proposes that coloour vision is mediated by three opponent system in the visual system, which respond to pairs of colours in an opposing manner

Red-green system - green and red as opposites

Blue-Yellow - blue and yellow as opposites

Black and White - lightness and darkness

supported by afterimages and inability to mix certain colours e.g redish green

occurs in the lateral geniculate nucleus

Colour constancy

ability to perceive an objects colour as remaining constant even under different lighting which influences the wavelengths

Chromatic Adaption - Habituation

Prolonged exposure to a specific light source causes the cones to sensitive to that wavelength to become less sensitive that helps balance out the colour contrast

Discounting the Illuminant

visual system estimates the colour of the light source and adjusts its perception of the object accordingly. allows perceived object as true colour regardless of ambient light

Simultaneous contrast

the appearance of colour is affected by the colours surrounding it

depth perception

our retina processes information in 2D, and allows us to perceive the world in 3D to accurately judge distances

brain uses various cues to infer depth from the 2D retinal image.

Oculomotor Cues

cues that rely on muscular movements of our eyes

• convergence - inward turning of the eye when we focus on a nearby object. uses the degree of convergence to judge the distance. Higher convergence = closer object

• Accomodation - change in shape of the lens to focus on objects at different distances. Muscular signals related to change are used to infer distance

• Limitations - these cues are only affective for objects within arms reach (2m) and are not strong depth cues

Monocular Cues / Pictorial Cues

cues that can be perceived with only one eye and are often used in 2D images or paintings to create illusion of depth

• occlusion/interposition - partial blocking of object, to show one that it is further away. Strongest cue

• Relative height - objects that are higher in optical are perceived to be further away

• Relative size - when object are the same size, the perceived smaller one is further away

• perspective convergence/linear perspective - parallel lines appear to converge at a distance, the closer the further away

• Familiar size - known actual size used to estimate the distance away

• Atmospheric Perspective - distant objects appear more densely packed the further away they are

• Texture Gradient - Regularly spaced elements appear more densely packed the further away they are

• Shadows

Motion based monocular cues

Motion parallax - when moving, close objects appear to be moving rapidly in the opposite direction, while far away objects move slowly in the same direction or remain relatively stationary

Binocular cues - Binocular disparity

the slight difference in the retinal image of the same object by the left and right eye

• Horopter - an imaginary arc passing through the fixation point, when objects fall on corresponding points in both eyes on this arc, there is zero disparity in the image

• non-corresponding points - disparity between the image in both eyes

• crossed disparity - occurs for objects closer than the horopter

• uncrossed disparity - object is farther than the horopter

binocular cues - stereopsis

vivid 3D perception of depth that result form the brain combining the two slightly different retinal images

Size Perception

ability to perceive objects actual size despite varying retinal image size due to differing distance

Pinna

visible part of the ear that helps localise sound

Auditory Canal

directs sound waves to the ear drum

Tympanic Membrane/ ear drum

Vibrates in response to sound waves

Ossicles

Three small bones that amplify and transmit vibrations frim the eardrum to the inner ear

Cochlea

fluid filled, snail shaped structure containing the organ of corti which houses hair cells

Hair cells

• hair cells - sensory receptors that convert mechanical vibrations into electrical signals

• inner hair cells - primarily responsible for transmitting sound information to the brain

• Outer hair cells - Ameliorate the transduction process and amplify the vibration of the basilar membrane increasing the sensitivity and sharpness of tuni

Basilar Membrane

vibrates in response to sound waves with different frequencies causing maximal vibration at different locations along its length

Auditory Pathway

Neural signals from the cochlea travel via the auditory nerve to the brain stem then to the thalamus and finally to the primary auditory cortex in the temporal lobe

Place theory

the pitch we perceive is determined by specific place on the basilar membrane that is maximally stimulated by sound wave.

Temporal coding

The pitch we perceive is determined by the rate of neural firing in the auditory nerve which matches the frequency of the sound wave.

• Phase locking - neurons fires at a specific phase of the sound wave

• Volley Principle - groups of neurons fire in volleys to represent higher frequencies even if the individual neurons cannot fire that fast

Azimuth/horizontal plane

determines by biaural cues/ both ears

• interaural time difference - difference in the time it takes for sound to reach each ear - effective for low frequencies

• Interaural level differences - the difference in sound intensity reaching each ear. effective for high frequencies

Elevation/ vertical plane

determined by monoaural cues/ one ear

• spectral cues - the pinna, modifies the frequency spectrum of incoming soinds differently depending on their elevation, creating characteristic notches in the sound frequency profile

Precedence Effect

Sound that is presented from two sources with a slight delay between them, simulation direct and indirect sound, listener perceives the sound as only coming for the first source which prevents echoes and allows us to localise sounds accurately in reverberant environments