Introduction to Physiological Psychology Psych 260 Kim Sweeney ksweeney@cogsci.ucsd.edu www.cogsci.ucsd.edu/~ksweeney/Psych260 Visual Agnosia Deficits in visual form perception NOT blindness! Caused by damage to visual association areas in ventral stream Video…. 1 Fusiform Face Area The fusiform face area (FFA) is part of the ventral (“what”) pathway. It’s located on the ventral surface of the temporal lobe. Prosopagnosia Damage to the fusiform face area (FFA) results in prosopagnosia. Diffusion tensor imaging (DTI) tractography reveals a reduction in the volume of the inferior longitudinal fasciculus in the brains of 6 patients with congenital prosopagnosia (top). (From Thomas et al 2008) 2 The lateral occipital complex is activated in response to a wide variety of objects. It seems possible that different categories of objects are processed at least in part in different subregions subregions.. Fusiform Face Area (FFA) Parahippocampal Place Area (PPA) Kanwisher et al (97-99) Tong et al (in press) Sergent et al (92) Haxby et al (91, 94, 99) Puce et al (95, 96) McCarthy et al (97) Halgren et al (99) Epstein & Kanwisher (98) Aquirre et al (98, 99) Haxby et al (99) Maguire et al (96, 97, 98) LOC: Things Malach et al. (95) Kanwisher et al. (96) Grill-Spector et al (98, 99) Kourtzi & Kanwisher (00) Body Area Downing et al (01) Drawing Modified from Allison et al (94) Also in the ventral stream is the extrastriate body area – Seems to be particularly responsive to body parts 3 The Auditory System 4 What is sound? If a tree falls in a forest and no one is there to hear it, would there be a sound? What is sound? If a tree falls in a forest and no one is there to hear it, would there be a sound? SOUND can refer to a physical stimulus or a perceptual response. – Physical stimulus: “sound” is pressure changes in air (or other medium) – Perceptual response: “sound” is the experience we have when we hear 5 What is sound? Auditory perception occurs when sound waves interact with the structures of the ear. Sound Wave—changes over time in the pressure of an elastic medium (e.g., air or water) – Without air (or another elastic medium), there can be no sound waves, and thus no sound. What is “color”? Hue – determined by wave length (red= longer, violet = shorter) Brightness – determined by amplitude Saturation – determined by purity 6 What is “sound”? Pitch- determined by the frequency of a Pitchvibration Loudness- determined by the amplitude Loudness(intensity) of a vibration Timbre- determined by the complexity of Timbrea vibration Frequency of Sound Waves The frequency of a sound wave is measured as the number of cycles per second (Hertz): 20,000 Hz 4,186 Hz 1,000 Hz 100 Hz 27 Hz Highest Frequency we can hear Highest note on a piano Highest pitch of human voice Lowest pitch of human voice Lowest note on a piano 7 Different animals are sensitive to different frequency ranges From Dusenbery, 1994 Intensity of Various Sounds (dB) Log P Decibels Softest detectable sound 0 Soft whisper 20 Quiet neighborhood 40 Average conversation 60 Loud music from a radio 80 Heavy automobile traffic 100 Very loud thunder 120 Jet airplane taking off 140 Loudest rock band on record 160 Spacecraft launch (from 150 ft.) 180 8 Timbre of various sounds Sound as a physical stimulus 9 Sound as a psychological experience Amplitude of a sound wave is related to loudness of a sound. Frequency of a sound wave is related to the pitch of a sound. Complexity of a sound wave is related to the timbre of a sound. sound. 10 What is “sound”? The relation between the physical and perceptual dimensions of sound 11 But how do we hear sound? Purpose of the structures in the ear: – Measure the frequency (pitch) of sound waves – Measure the amplitude (loudness) of sound waves 12 Major Structures of the Ear Outer ear (Pinna (Pinna))—acts as a funnel to direct sound waves towards the tympanic membrane and inner ear structures Middle ear— ear—consists of three small bones (or ossicles) ossicles) that amplify the sound Inner ear— ear—contains the structures that actually transduce sound into neural response Anatomy of the Ear 13 Audition in three easy steps Sound is funneled via the pinna (external ear) through the ear canal to the tympanic membrane (eardrum), which vibrates with the sound The middle ear (located behind the tympanic membrane) includes the middle ear bones, the ossicles (malleus malleus,, incus and stapes) The malleus connects with the tympanic membrane and transmits vibrations via the incus and stapes (at the oval window) to the cochlea (inner ear), the structure that contains the receptors The Ear Sound wave > eardrum > ossicles > oval window Vibration of the oval window sets in motion the fluid of the cochlea The cochlea’s internal membrane, the organ of Corti,, is the auditory receptor organ Corti 14 The Cochlea The cochlea is part of the inner ear; it is filled with fluid, therefore sounds transferred through the air must be transferred into a liquid medium; the ossicles aid in this transmission Within the cochlea, there are three separate chambers: Scala vestibuli Scala media Scala tympani 15 The Cochlea The organ of Corti is found in the middle chamber- scala media The organ of Corti consists of – Basilar membrane (the base) – Tectorial membrane (the roof) – Hair cells in between Hair cells within the organ of Corti transduce sound waves into nerve impulses – Inner hair cells are crucial for hearing, outer hair cells enhance inner hair cells’ sensitivity Hair Cells, or Cilia In the human cochlea we find TWO kinds of hair cells: Inner hair cells – Responsible for hearing (95% of afferent info) Outer hair cells – Responsible for amplifying soundsound- they can move, so amplify basilar membrane movement 16 Auditory Hair Cells Inner hair cells: (~ 3500) form a single line of cells along the basilar membrane Destruction of inner hair cells eliminates hearing Outer hair cells: (~ 12,000) are arranged in three rows along the basilar membrane Outer hair cells serve a structural function The cilia project from the top of each hair cell The tectorial membrane is attached to the (some of the) outer hair cell cilia When sound waves move the basilar and tectorial membranes, the cilia bend in one direction or the other Shear of the cilia generates a receptor potential that releases a neurotransmitter 17 The Basilar Membrane Sound waves cause the basilar membrane to move relative to the tectorial membrane, which bends the cilia of the hair cells… this bending produces receptor potentials!! Because of the physical properties of basilar membrane: tonotopic organization Cilia are connected by tip links 18 Auditory Transduction Cilia tips are joined by fiber links Cilia movement produces tension of the link which opens (or closes) ion channels in the adjacent tip Calcium and potassium ions produce a depolarization or hyperpolarization 7.37 19 Auditory Transduction Movement towards the tallest cilium result in depolarization: – Higher firing rate Movement away from the tallest cilium results in hyperpolarization: – Lower firing rate Sound Transmission Through the Ear 20 Sound Transmission Through the Ear Sound Transmission Through the Ear 21 Sound Transmission Through the Ear Sound Transmission Through the Ear 22 Cochlear Coding Different frequencies produce maximal stimulation of hair cells at different points along the basilar membrane Tonotopic (frequency) organization exists not only at the basilar membrane but also in most other parts of auditory system 23 Tonotopic OrganizationOrganization- Place Coding Tonotopic Organization 24 Distinguishing Pitch Place theory— theory—different frequencies cause larger vibrations at different locations along the basilar membrane (place coding) Frequency theory— theory—basilar membrane vibrates at the same frequency as the sound wave (rate coding) 25 Pitch perception: Place coding The cochlea has a tonotopic organization For high frequencies Pitch Perception: Rate code Used for low frequency sounds ( <1500 Hz ) Mechanism: The rate of neural firing matches the sound's frequency. For example, – 50 Hz tone (50 cycles per sec) -> 50 spikes/sec, – 100 hz -> 100 spikes/sec Problem: even at the low frequency range, Problem: some frequencies exceed neurons’ highest firing rate (200 times per sec) Solution:: large numbers of neurons that are Solution phased locked (volley principle). 26 Then what? Sound is processed both ipsilaterally and (especially) contralaterally Then what? Cochlear nerve> cochlear nucleus of medulla > superior olive > inferior colliculus> colliculus> MGN (thalamus!) > Primary auditory cortex Efferent information from inferior colliculus 27 Subcortical Mechanisms of Sound Localization The lateral and medial superior olives react to differences in what is heard by the two ears – Medial – arrival time differences – Lateral – amplitude differences Both project to the superior colliculus – The deep layers of the superior colliculus are laid out according to auditory space, allowing location of sound sources in the world; the shallow layers are laid out retinotopically – … so it seems that function is identifying location Anatomy and function Many sound features are encoded before the signal reaches the cortex - Cochlear nucleus segregates sound information - Signals from each ear converge on the superior olivary complex important for sound localization - Inferior colliculus is sensitive to location, absolute intensity, rates of intensity change, frequency important for pattern categorization - Descending cortical influences modify the input from the medial geniculate nucleus - important as an adaptive ‘filter’ cortex medial geniculate body inferior colliculus cochlear nucleus complex cochlea superior olivary complex 28 Sound Localization Interaural Intensity Difference (high frequency) Interaural Time Difference (low frequency) Spatial Location of Sound Auditory neurons in the superior olives detect phase differences 29 Perception of Spatial Location Arrival time difference for high frequency sound “What” and “Where” pathways Just as in the visual system, the auditory system seems to have separate pathways for analyzing the location and the identity of a sound. Just as in the visual system, the “where” pathway is more dorsal, and the “what” pathway is more ventral. 30 Evidence for “top“top-down” processing in the auditory system Next time… – The vestibular system – Gustation and Olfaction – !! Somatosenses AFTER all this other stuff! 31