PSYC3460 Final EXAM - Summary Sensation and Perception PDF

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Summary

Detailed summary of course content for the final exam. ...

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MOTION Motion blindness (akinetopsia) -

Caused by lesion covering substantial region of the VISUAL CORTEX (including V5/MT aka middle temporal visual area)

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Stationary objects appear stationary but when object or person moves, it disappears. When objects stop moving, it reappears.

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Can lead to Inability to follow a continuous motion such as pouring liquid, difficulty following speech, problems tracking who is coming and going and crossing the street is impossible

Why is motion important? -

Separation of figure and ground; contrast between figure and background. Without movement it is hard for us to figure out background

Types of motion -

Real motion: the object you behold moves

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Apparent motion: illusory motion between two alternatively flashing lights

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Induced motion: motion of one object (large clouds) causes another object (small moon) to appear to be moving

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Motion after effects: prolonged viewing of a moving stimulus (flowing water) causes percept of motion in opposite direction

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Progression motion: appears to be a single dot jumping back and forth between two locations, but it is really 2 dots turning on and off

How do we perceive motion? -

Motion perception depends on movement across the retina.

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Gibson pioneered the ecologcal approach to perception. -

Focused on the optic array (all info in visual enviro)

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Optic array changes when things move and when we move

Corollary discharge theory -

Takes into account how image moves across retina and how eyes move also

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Motion perception depends on three signals: 1. An image displacement signal: the motion of the stimulus on the retina. Signal that occurs when image moves across visual receptors 2. The motor signal: sent to the eye muscles which tells the eyes how to move 3. The corollary discharge theory: a rpediction of the sensory outcomes that will result from the enactment of the motor signal

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A prediction about how will my eyes feel, where will I be looking, and how will the images slide across the retina. The use of these 3 signals can determine what is moving and what is stationary.

How do neurons code motion direction? -

Hubel and Weisel varied the orientation and direction of motion of bars to find what combination made that a V1 cell fire at its maximum rate

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Shows that motion direction can be ambiguous if your stimulus is a bar

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MOTION PERCEPTION WITH FIELDS OF DOTS

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Monkeys were taught to judge motion coherence while activity was monitored in a group of MT neurons

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As coherence increased, so did accurace (behaviour) and firing rates (brain).

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Lesioning MT increased the amount of coherence necessary to accurately detect motion direction suggesting a relationship between physiology and perception

Neural pathways for motion -

Proposal: V1 neurons converge onto MT neurons

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70ms after motion stimulus is shown, MT neurons respond to orientation, not direction. However, after 140ms, MT neurons begin to respond to direction of motion. Therefore, MT neurons need time to get info from many V1 neurons to resolve the direction of motion.

Biological motion -

The movement of a person of living thing. We are remarkably sensitive to human motion.

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When observing point- light walkers, you can identify yourself faster and more accurately than you can identify your friends

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Grossman and Blake (2002) have argued that superior temporal locus is involved in processing biological motion

Predicting intentions -

Mirror neurons may help understand another animal’s actions and react to them/ help imitate the observed action

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Mirror- neuron like responses in the human brain can be influenced by intention

Learning by observation -

Social: courtesy, attitudes

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Cognitive: strategy

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Perceptual: what success looks and sounds like

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Motor: movement dynamics

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OBSERVATION SYSTEM: -

F5 neurons respond to object- directed action

COLOUR AND DEPTH HUE -

Colour of target

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The quality that distinguishes red from green from yellow

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Physical: wavelength

SATURATION (dilution) -

Degree to which hue is diluted by white

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Characterizes a colour as pale, vivid, or something in between

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Physical: spectral purity

BRIGHTNESS -

The perceived intensity of the target

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Physical: luminance

Trichromatic theory -

Describes how wavelength info is captured by retina. Colour vision depends on the activity of three different receptor mechanisms

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Psychophysical evidence: colour matching experiences- any colour can be matched using 3 wavelength

Physiological support for trichromatic theory -

Identification of 3 types of cone pigments -

S cones respond to short wavelengths

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M cones respond to middle wavelengths

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L cones respond to long wavelengths

Are 3 receptors necessary to see colour? -

People with 3 cone types= trichromats (normal)

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Two cone types= dichromats. See colour but not the range

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Protanopia- long wavelength (L cones missing)

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Deuteranopia- medium wavelength missing

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Tritanopia- likely altered short wavelength cones

Monochromats have one cone type or non (colourblind) -

Principle of univariance: one receptor would respond to light but it would only signal changes in intensity

Opponent process theory -

Based on people’s experience when looking at colour paintings.

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Simultaneous contrast: happens when an image is surrounded by another colour so it appears to be a different colour than it actually is

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Visual system interprets colour signals from cones in antagonistic manner

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Found colour- opponent receptive fields in LGN as well as colour- opponent cells later identified in monkey cortex

Determining depth and size 1. Oculomotor cues: sensing the muscle tension around our eyes a. Occlusion: closer objects obscure more distant ones 2. Binocular cues: difference in the position of images in the two eyes. Our brain converts overlapping 2D images on the retina into a 3D model of the world 3. Static cues: shows depth in 2D photos. These cues are monocular because they still work and can be recognized with one eye (systematic relationship with depth)

SIZE AND HEARING Size distance scaling: direct relationship between size and distance- if retinal size is constant, a closer object will be perceived as smaller than a further object size constancy: our perception of an object’s size remains relatively constant even when we view it at different distances (which changes the retinal image size) -

Size constancy allows for the accurate perception of real size despite changes in the size of the retinal image

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When depth info is absent or difficult to determine, we often make mistakes (illusions)

Depth for size perception Do observers perceive the real size or the retinal image size? -

If P rely on retinal size, the size of circle should always look the same

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If P relies on real size, size of circle should look bigger when it is further away

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As depth cues were eliminated, perceived size was closer to the retinal size 1. Many depth cues- ps report physical size of circle (not retinal size) 2. One- eyed viewing- removes all stereoscopic depth information (binocular disparity) 3. Viewing through a peep- hole removes many monocular depth cues 4. Drapes used to eliminate reflections and shadows- removes even more depth cues- now ps reports are closer to the retinal size

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Our ability to judge size depends on depth depth -

EX the sun and moon have the same size in the retina but the moon is smuch smaller and so much closer. But we are really bad at judging distance of the sun, moon, stars etc so we rely entirely on retinal image size

Size perception -

Relative size and texture are useful cues when size is ambiguous

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Familiar size plays a large role in size perception, especially for things we know very well like humans

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Perception that two figures are roughly the same size despite difference in retinal image and size consistency

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Size distance scaling: if two objects have the same retinal image size, the one that appears closer will look smaller

Functions of hearing -

Releases our dependence on vision by adding redundancy

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Alerts us to dangers we cannot see

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Facilitation of communication (hellen keller)

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If a tree falls and no one is there to hear it, does it make a sound? -

If you define sound as the physical stimulus

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If your define sound as the conscious experience

The sound stimulus -

A change in the pressure of the surrounding medium (usually air but can be any fluid)

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Achieved with any vibrating surface

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Molecules of air alternately compressed and released

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Note that it is compression that travels through space, not the air molecules themselves

Signal amplitude and frequency -

amplitude= loudness

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Sensitive to a very wide range of amplitudes between threshold for detection and threshold for pain

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How do we measure amplitude? Decibel units. Unusual because it is not an absolute value, it is a ratio

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Signal frequency: pitch -

Tone height is the experience of increasingly higher pitches

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Notes on the keyboard with the same letter have the same tone “chroma”

Complex tones vs. pure tones Timbre: the perception of two sounds with the same loudness and same pitch as dissimilar -

Trumpet and paino both play a C note at the same dB level

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Conveyed by haronics and other high frequencies

Pure tones: a sound composed of a sine wave with a single frequency component Complex tones: tones with multiple frequency components and harmonics -

harmonics= all frequency components in a complex tone

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Fundamental frequency= lowest frequency component of a tone

EAR AND LOCALIZATION AND SPEECH -

The ear and auditory processing system codes pitch ,amplitude, and spectrum

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Pitch and timbre coding and perception- basilar membrane and cortex

Structure of the ear (look at ipad) -

External ear -

Pinna: directs sound into auditory canal and prioritizes sound

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Auditory canal: funnels and amplifies incoming sound

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Tympanic membrane: converts air pressure changes into mechanical vibrations

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Middle ear -

Amplifies and transmits vibrations of tympanic membrane to the inner ear

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Accomplished by the ossicles, malleus, incus, and stapes.

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Force fussing device- eardrum has much larger surface area than stapes

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Lever- malleus moves further than stapes

Inner ear -

Has 2 main components: cochlea (hearing) and semicircular canals (vestibular system)

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Stapes attaches to cochlea at oval window

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Structures of the inner ear amplify and transduce signal

COCHLEA -

3 canals in fluid- filled cochlea 1. Vestibular canal 2. Scala media (middle canal) 3. Tympanic canal

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Basilar membrane forms base of scala media

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Organ of corti- analogue of retiha -

Rests on basilar membrane

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Site of neural transduction

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Contains hair- cell receptors ( sensory receptors for hearing)

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Motion of stapes against oval window moves the fluid in the cochlea

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Pressure waves rolls through vestibular canal, moves basilar membrane

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Shearing motion of hair cells generates neural signals, transmitted by auditory nerve

Place theory for coding pitch -

George von bekesy observed the movement of the basilar membrane direction

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The location of the wave peak varies with frequency

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Fourier analysis breaks complex waveforms into their component frequencies

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Cochlea achieves this through place coding

Primary auditory pathway -

Auditory nerve cells (cochlea) project to brain centres

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Ascending pathways pass through several different nuclei before reading cortex

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All information leaving ear projects bilaterally

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There are stronger projections to the contralateral hemisphere

Auditory localization- cues etc. -

Auditory localization: determining the direction and distance of the sound source

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Auditory scene analysis: determine which sounds belong to which source

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Two classes of direction cues: binaural and monaural -

Monaural: cues for determining direction that are available to a single ear -

Pinna- the distinctive shape of the pinna causes sounds to be reflected back and forth in the folds

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Spectral cues: experiments where the pinnae are flattened against the head or the nooks are filled in

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At first elevation judgements suffered much more than azimuth judgement. They found that people adapted to the moulds, and their performance improved over time

- relationship between spectral cues and elevation are learned, and can be relearned....