Sensation and Perception 2

• Helps classify and identify objects
• Facilitates perceptual organisation of elements into objects
• May provide an evolutionary advantage in foraging food

• Basic colours: red yellow green blue
• Changed by intensity, saturation, wavelength
• violet- blue-green-yellow-orange-red
• Colour of objects are determined by the wavelength that are reflected
• See white: reflection of all colour wavelengths
• Black: little light reflected

• Young and Helmholtz (18800's)
• Three different receptor mechanisms are responsible for colour vision
• Behavioural evidence
• Colour matching experiments: shine light in front of desk (one wave length) other desk, different wavelength lights. Had to match the 3 different wave lenths to match the first. 
• Used to show that most people need three of the wavelengths to create a match

• Researchers measured absorption spectra of visual pigments in receptors (1960's)
• they found 3 types of cones pigments responded maximally to: 
• short wavelengths (419nm)
• Medium wavelengths (534 nm)
• Long wavelengths (564 nm)

• Only rods and no functioning cones
• Ability to perceive only in white, gray and black tones
• Poor visual acuity
• Sensitive to bright light

• 3 types
• Protanopia: individuals see short wavelengths as blue
• Neutral point occurs at 492 (grey instead of green)
• Above neutral point, they see yellow then grey instead of red
• Missing the long wave length pigment
• Deuteranopia: see short WL as blue
• Neutral point occurs at 498nm (grey instead of green)
• Above neutral point, they see yellow.
• Can detect red, but seen as yellow
• Tritanopia (blue yellow colour blind): see short WL as blueish green
• Neutral point occurs at 570nm (no yellow)
• Above neutral point, see red
• Probably missing the short WL pigment.

• Proposed by Hering (1800s)
• Colour vision is caused by opposing responses generated by blue and yellow and by green and red
• Behavioural evidence:
• Types of colour blindness red/green and blue/yellow
• Colour afterimages and simultaneous colour contract show opposing pairings

• Focuses on information int he retinal image that is correlated with depth in the scene
• Oculomotor cues are based on sensing the position of the eyes and muscle tension
• Occular convergence: inward movement of the eyes when we focus on nearby objects. Associate tense w/ close objects
• Accomodation: change in the shape of the lens when we focus on objects at different distances

• Monocular (pictorial) cues come from one eye .
• Sources of depth information that come from 2D images such as pictures
• Occlusion/interposition: when one object partially covers another
• Relative size: when objects are equal size, the closer one will take up more of your visual field
• Perspective convergence/linear perspective: parallel lines appear to come together in the distance
• Familiar size: distance information based on our knowledge of object size
• Atmospheric perspective: distance objects are fuzzy and have blue tint (on clear day)
• Texture gradient: equally spaced elements are more packed as distance increases
• Shadows: indicate where objects are located

Motion parallax: close objects in direction of movement glide rapidly past but objects in the distance appear to move slowly

• Binocular disparity: difference in images from two eyes.
• Left and right eye transmit different information, allowing us to perceive depth

• Non veridical perception occurs during visual illusions
• Muller-lyer illussion: straight lines with inward fins appear shorter than straight lines with outward fins
• Ponzo illusion: horizontal objects are placed over railroad tracks in a picture. Upper object appears larger
• Ames room: two people of equal size appear very different in size in this room
• Room is constructed so that the shape looks like a normal room when viewed with one eye

• Sounds is created by pressure changes in the air or other medium
• Sound is the experience we have when we hear

• Pure tone: created by a sine wave. 
• Amplitude: height. How much air pressure change. Loudness (db)
• Frequency: number of cycles in a given time period (Hz). Pitch
• Complex tone: mixture of tones together

• All other perceptual aspects of a sound besides loudness, pitch and duration
• Reflects the number and magnitude of harmonics
• It is the 'quality' or 'complexity' of a sound

Frequency of sound is indicated by the place on the organ of corti that has the highest firing rate

• Auditory space: surrounds an observer and exists wherever there is sound
• Sounds are localised in space by using:
• Azimuth coordinates: position left to right
• Elevation coordinates: position up and down
• Distance coordinates: position from observer

• Binaural cues: location cues based on the comparison of the signals received by the left and right ears
• Interaural time difference: difference between the times sounds reach the two ears
• When distance to each ear is the same, there are no differences in time
• When the source is to the side of the observer, the time will differ
• Interaural level difference: difference in sound pressure level (volume) reaching two ears
• Reduction in intensity occurs for high frequency sounds for the far ear

• Detect elevation
• Uses shape of Pinna

• Auditory scene: the array of all sound sources in the environment
• Auditory scene analysis: process by which sound sources in the auditory scene are separated into belonging to individual perceptions/streams

• Heuristics that help to perceptually organise stimuli
• Onset time: sounds that start at different times are likely to come from different sources
• Location: a single sound source tends to come from one location and to move continuously
• Similarity of timbre and pitch: similar sounds are grouped together
• Proximity in time: sounds that occur in rapid succession usually come from the same source
• Auditory continuity: sounds that stay constant or change smoothly are usually from the same source