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Final Review

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McGill University
PSYC 212
Evan Balaban

CHAPTER SEVEN THEAUDITORY SYSTEM: MUSICAND SPEECH PERCEPTION • Musical instruments have multiple resonant qualities ◦ produce complex tones that contain a fundamental frequency ◦ produce a set of harmonics that are exact multiples of the fundamental ◦ despite this, instruments produce a single pitch sensation (musical pitch) ▪ equivalent to the pitch associated with the fundamental frequency ▪ it is believed that the spatial arrangement of wave patterns on the basliar membrane produced by the harmonics is responsible for their coherence into a single pitch sensation • octave ◦ 2:1 frequency ratio ▪ represents the fundamental interval of musical pitch ◦ effective range of musical pitch spans seven octaves ▪ beyond this range, the harmonics are no longer suitable as musical sounds ◦ an octave can be further divided into intervals, called notes ▪ positions of notes in an octave – chroma • equally tempered scale – established by Bach ▪ Western musical culture ▪ broken into 12 equal divisions known as semitones • musical notes are represented by staff notation ◦ allows musicians to play music without knowing pitch composition • musicians have a well-developed sense of relative pitch as a result of listening to and playing tonal sequences • perfect pitch – ability to identify an isolated tone by name, is much more difficult ▪ 1:10,000 • timbre – a difference in tone quality ◦ arises from difference intensity distributions of the harmonics • each instrument has its own characteristic intensity distribution for each harmonic of a note ◦ causes subtle differences in the neural activation at the respective points in the basilar membrane ▪ three major categories of musical instruments: • chordophones • aerophones • percussions • music relies on two distinct qualities: ◦ tonal superpositions (simultaneous appearance of musical tones) ◦ tonal sequences (sequential appearances of musical tones) • auditory system is able to distangle the individual components of a musical note in a superposition, such as a chord, and associate them with an individual note ◦ constant superpositions occur when they sound pleasant ◦ dissonance arises from harsh and clashing combinations ▪ arise when two or more tones produce interference among their activational patterns on the basilar membrane ◦ tonal sequences are responsible for the melodic quality of music, whih in turn creates rhythm and tempo ◦ the sequential sound pattern of music resonates with some internal rhythm in the brain that in turn leads to the activation of higher emotional centres • three areas of research on speech perception: ◦ speech production ◦ speech comprehension ◦ brain structures responsible for each • speech is the only structured sensory stimulus produced by humans ◦ vocalization process leading to speech involves the subglottal system, larynx, and vocal tract ▪ vocal folds (glottis) are controlled by muscles during exhalation to produce a buzz- like sound that is the shaped by different structures of the vocal tract to produce the audible sounds of speech • speech can be broken down into words ◦ words can be broken into syllables ▪ syllables are broken into phonemes • phonemes are the smallest unit of speech ◦ can be represented symbolically by a single character • speech can be represented by its pressure waveform ◦ this does not contain frequency information ▪ sound spectrograph – provides a visual display of frequency as a function of time • intensity is represented by the darkness of the markings on the graph • specific phonemes appear as bands of resonant frequencies called formants • vowel sounds are composed of low frequencies and appear near the bottom of the spectrograph • consonants are made up of higher frequencies that appear near the top • all human languages are structured, symbolic, and arbitrary systems • the goal of psycholinguistic research is to understand the mechanisms that underline human language use ◦ sentences are broken down into four different processing stages: ▪ words, sounds, and non-speech sounds must be isolated and recognized (sensory perception) ▪ words must be identified and their meanings understood (cognitive psychology) ▪ grammatical rules must be applied to derive meaning from a sequence of words (cognitive psychology) ▪ meaning must then be interpreted within the specific context (cognitive psychology) • the unique human ability of speech expression and comprehension arieses due to the presence of the specialized brain areas dedicated to language ◦ Wernicke's aphasia ▪ ability to speak ▪ inability to understand language ▪ damage to Wernicke's area – speech recognition/comprehension area (L hemisphere) ◦ Broca's aphasia ▪ slurred and slow speech ▪ maintenance of language understanding ▪ damage to Broca's area – speech production area (L hemisphere) CHAPTER EIGHT THE VISUAL SYSTEM: LIGHT, OPTICS,AND THE EYE • for many centuries, it was believed that light was made up of particles ◦ many aspects of light cannot be explained this way • dual-theory ◦ light travels both like a particle and a wave ▪ composed of particles that travel in a wave-like manner • light is an example of electro-magnetic radiation ◦ electro-magnetic radiation – moving energy field consisting of both oscillating electrical and magnetic fields ▪ wavelength - a full cycle of the electric field • visible light spans the wavelength of 400-700 nm ◦ blue – short wavelengths ◦ green and yellow – middle wavelengths ◦ red – long wavelengths • it is convenient to consider light as emanating form a point source when describing its interaction with objects ◦ optical infinity – a distance of 20 ft. (6m) from the point source, the divergence of light rays becomes so negligible that they can be considered parallel ▪ represents the initial condition when examining the interaction of light with objects • light can be absorbed, reflected, or scattered by an object ◦ light can also be transmitted through transparent objects • refraction – phenomenon that arises at the border between two different media ◦ causes the light rays to converge or diverge away from the normal (the plane perpendicular to the boundary) ▪ the greater the difference in refractive index between the two media, the greater the refraction at the boundary • the curved surface of a lens are ideally suited for refraction ◦ with a concave lens, light rays are refracted so they emerge from the lens in a divergent manner ▪ can never create a true image of the point source ◦ with a convex lens, light rays are refracted so they emerge from the lens in a convergent manner ▪ produces a true image at a certain distance away from the lens • distance depends on the optical power of the lens ◦ optical power of the lens is determined by the curvature of the lens surfaces and the refractive index of the lens ▪ image distance increases as the object is brought closer to the lens • the eye is made up of many components, notably the cornea, crystalline lens, aqueous and vitreous humours, and retina • the eye is both an optical instrument and a device that converts the energy in visible light into neural signals • optical properties arise at the air-cornea surface by way of the crystalline lens • emmetropic eye – one whose optical power is precisely sufficient to converge light rays from a point source at optical infinity into an image on the retina ◦ the retinal image is inverted and horizontally flipped • objects located closer than optical infinity require the eye to increase its optical power in order to create a focused image on the retina ◦ accomplished by the process of accommodation ▪ an increase in the surface curvature of the lens surfaces to provide extra optical power ▪ a reflex process driven by the blur signal on the retina ▪ there is a limit to how much accommodation is possible • objects closer than the near point cannot be accommodated and remain out of focus • presbyopia – arises from reduced elasticity of the lens with increasing age ◦ leads to decreased accommodative ability • hyperopia (farsightedness) – arises when the eyeball is too short for the optical power of the eye ◦ eye accommodates to provide the additional optical power to see distant objects, but this reduces the overall accommodative capabilities of the eye ▪ can be corrected by wearing glasses with a positive optical power (convex lens) • myopia (nearsightedness) – arises when the eyeball is too long for the optical power of the eye ◦ can be corrected by wearing glasses with a negative optical power (concave lens) CHAPTER NINE THE VISUAL SYSTEM: RETINAL PROCESSING AND EARLY VISION • an optically normal eye creates a visual image directly on the retina and, more specifically, upon the retinal layer that is lined with photoreceptors ◦ photoreceptors are able to capture light photons and subsequently create a neural signal ▪ rod photoreceptors – specialized for low light conditions • density distribution profile is highest in the periphery ▪ cone photoreceptors – function at much higher light levels • density is highest in the fovea (center of the retina) • three kinds of cone receptors are responsible for generating color vision • absorption spectrum of rods shows a maximum at 500 nm ◦ coincides with the maximum spectral sensitivity of scotopic vision • three cone subtypes each have different peaks of absorption ◦ S-cones – 440 nm ◦ M-cones – 530 nm ◦ L-cones – 560 nm ▪ three cones form the foundation for scotopic vision • peak spectral sensitivity at 550 nm • rods have lower activation threshold than cones and become bleached at moderate to high light intensities ◦ cone bleaching only occurs at high light intensities • the retina is anatomically composed of three layers ◦ photoreceptor layer ◦ inner nuclear layer ◦ ganglion cell layer • axons of ganglion cells leave the eye and carry retinal signals to higher centres of the brain ◦ two major types of ganglion cells ▪ midget – small cell size; small dendritic field ▪ parasol – large cell size; large dendritic field • the area of the retina that can influence a ganglion cell is called the receptive field • ganglion cells display circular receptive fields with either ◦ a central excitatory and surrounding inhibitory zone (ON/OFF) OR ◦ a central inhibitory and surrounding excitatory zone (OFF/ON) ▪ the antagonistic nature of this arrangement is optimally suited for visual contrast detection • the central retina has a foveal pit where the neurons of the inner nuclear layer and ganglion cells are shifted to one side, giving light rays more direct access to the photoreceptors • the wiring pattern of photoreceptors to ganglion cells varies across the retina ◦ in the central retina, the wiring is so fine that it may be possible to have a single photoreceptor connected through a bipolar cell to a single ganglion cell ▪ this arrangement is responsible for the finest degree of spacial sampling and largely accounts for the high resolution (and poor sensitivity) of central vision ◦ in the peripheral retina, there is a great convergence whereby a single ganglion call is driven by a much larger array of photoreceptors ▪ this arrangement is largely responsible for the high sensitivity (and poor resolution) of peripheral vision • visual resolution (acuity) can be affected by a number of factors, including point-spread functions and image location (fovea vs. periphery) ◦ acuity generally declines with retinal eccentricity ◦ Snellen chart – simplest measure of spatial resolution ▪ more detailed test involves contrast detection for gratings of different spatial frequencies • resulting contrast-sensitivity function shows a peak around 8-10 cycles/degree for normal vision • scotopic (rod) vision is different from photopic (cone) vision in the following ways: ◦ scotopic vision ▪ mediates by one receptor type ▪ generates monochromatic (greyscale) vision ▪ dominant in the peripheral retina ▪ has a low activation threshold ▪ peak spectral sensitivity around 500nm ▪ rods have a high degree of neural convergence • produce vision that is of low resolution but high sensitivity ◦ photopic vision ▪ mediated by three different cone subtypes ▪ generates color vision ▪ dominant in the central retina ▪ higher activation threshold than rods ▪ peak spectral sensitivity around 550nm ▪ much lower degree of nerual convergence • produce vision tha is of high resolution but low sensitivity • the centre-surround properties of ganglion cells are responsible for a number of perceptual phenomena ◦ lightness contrast – arises when an object appears to be of different lightness depending upon the background ▪ direct consequence of the surround inhibitory influence upon the neural output of a ganglion cell ◦ lightness constancy – responsible for the similarity of lightness appearance of an object under different environmental light conditions ▪ the coincident effect on both the centre and surround response of a ganglion cell under varying light levels is responsible for the constancy in signal output CHAPTER TEN THE VISUAL SYSTEM: CORTICAL PROCESSINGAND OBJECT PERCEPTION • the major target of the retinal fibres emerging out of the eye is the lateral geniculate nucleus (LGN) ◦ six layered subcortical structure ◦ located in the thalamus • from the LGN, signals are carried by the optic radiation to the primary visual cortex in the occipital lobe • retinal output is split into a nasal half and a temporal half ◦ temporal fibres project to the LGN on the same side ◦ nasal fibres cross over at the optic chiasm before projecting to the opposite LGN ▪ this layout ensures that the right visual field is represented in the left cerebral hemisphere and the left visual field is represented in the right cerebral hemisphere • the bottom two layers of the LGN (layers 1 and 2) have large cell bodies and are known as the magnocellular (M) layers • the top four layers of the LGN (layers 3 to 6) have smaller-sized neurons and are referred to as the parvocellular (P) layers • LGN neurons have similar receptive field structures as retinal ganglion cells ◦ centre-surround antagonism ▪ ON/OFF or OFF/ON organization • the LGN displays a precise retinotopic organization • the superior colliculus (SC) receives projections from the retina, as do a number of other subcortical structures ◦ SC is involved in integrating sensory and motor information for the guidance of eye movements • primary visual cortex (area V1) ◦ has six layers ▪ labelled from top (layer 1) to bottom (layer 6) ▪ somewhat distorted retinotopic map, but with much larger foveal representation ▪ four new features arise in area V1: • binocularity ◦ area V1 neurons integrate retinal output from the two eyes ◦ binocular neurons fire optimally when both eyes are stimulated ◦ important for depth perception • orientation selectivity ◦ area V1 neurons have elongated receptive fields optimally suited for coding the orientation of a light bar or an edge ▪ different neurons have differing degrees of orientation selectivity ▪ Hubel and Wiesel • theorized that the summarized input of neurons with circular receptive fields oriented along a particular axis likely represents the basis for orientation selectivity • directional selectivity ◦ a subset of area V1 neurons displays a preference for stimuli moving in a particular direction ◦ a majority of neurons are equally responsible to all directions of movement • color contrast selectivity ◦ a subset of area V1 neurons can distinguish pure color differences in the stimulus • the functional architecture of area V1 is such that a vertical set of ocular dominance columns is arrayed in conjunction with another set of vertical columns for orientation preference • Hubel and Wiesel's ice-cube model ◦ the two sets of columns have a perpendicular relationship ◦ a hypercolumn spans a full set of orientation columns and one pair of ocular dominance columns • the M- and P-channels originate in the retina and remain segregated through the LGN and into the input layers of area V1 • lesion studies of the M- and P-layers of the LGN have revealed that two pathways serve very different functional requirements • M-pathway ◦ low colour sensitivity ◦ low spatial resolution ◦ high temporal sensitivity ◦ best suited to process dynamic stimuli • P-pathway ◦ high colour sensitivity ◦ high spatial resolution ◦ low temporal sensitivity ◦ best suited to process static stimuli upon which a considerable amount of image (and color) detail can be processed • general characteristics of the M- and P-pathways appear to be maintained to some degree throughout the extrastriate cortical areas ◦ areas MT and V4 serve as major gateways to a host of visual areas ▪ MT – PARIETAL LOBE – DORSAL STREAM • these areas display qualities consistent with an M-channel link ▪ V4 – TEMPORAL LOBE – VENTRAL STREAM • these areas display qualities consistent with a P-channel link
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