Copyright © 2009 Allyn & Bacon Chapter 7: Mechanisms of Perception – Hearing, Touch, Smell, Taste, and Attention How You Know the World This multimedia product and its contents are protected under copyright law. The following are prohibited by law: any public performance or display, including transmission of any image over a network; preparation of any derivative work, including the extraction, in whole or in part, of any images; any rental, lease, or lending of the program. Copyright © 2009 Allyn & Bacon

The Case of the Man Who Could See Only One Thing at a Time This chapter focuses on the four exteroreceptive sensory systems besides vision that interpret external stimuli Why would a man be unable to see two objects simultaneously when he can see each individually? What could cause this deficit? Copyright © 2009 Allyn & Bacon

Principles of Sensory System Organization Primary – input mainly from thalamic relay nuclei For example, striate cortex receives input from the lateral geniculate nucleus Secondary – input mainly from primary and secondary cortex within the sensory system Association – input from more than one sensory system, usually from secondary sensory cortex Copyright © 2009 Allyn & Bacon

Principles of Sensory System Organization (continued) Hierarchical organization Specificity and complexity increases with each level Sensation – detecting a stimulus Perception – understanding the stimulus Functional segregation – distinct functional areas within a level Parallel processing – simultaneous analysis of signals along different pathways Copyright © 2009 Allyn & Bacon

Copyright © 2009 Allyn & Bacon Two models of sensory system organization Copyright © 2009 Allyn & Bacon

Copyright © 2009 Allyn & Bacon Auditory System: Sound The relation between the physical and perceptual dimensions of sound Copyright © 2009 Allyn & Bacon

Copyright © 2009 Allyn & Bacon The Ear Sound waves enter the auditory canal of the ear and then cause the tympanic membrane (the eardrum) to vibrate This sets in motion the bones of the middle ear, the ossicles, which trigger vibrations of the oval window Copyright © 2009 Allyn & Bacon

Copyright © 2009 Allyn & Bacon The Ear (continued) Semicircular canals Auditory Nerve Cochlea (unwound) Round window Oval window Tympanic membrane Tectorial membrane Hair cells Organ of Corti Basilar membrane Anatomy of the ear Auditory nerve Copyright © 2009 Allyn & Bacon

Copyright © 2009 Allyn & Bacon The Ear (continued) Sound wave > eardrum > ossicles (hammer, anvil, stirrup) > 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 Copyright © 2009 Allyn & Bacon

Copyright © 2009 Allyn & Bacon The Ear (continued) Organ of Corti Composed of two membranes Basilar membrane – auditory receptors, hair cells, are mounted here Tectorial membrane – rests on the hair cells Stimulation of hair cells triggers action potentials in the auditory nerve Copyright © 2009 Allyn & Bacon

Copyright © 2009 Allyn & Bacon The Ear (continued) Cochlear Coding Different frequencies produce maximal stimulation of hair cells at different points along the basilar membrane Tonotopic (frequency) organization of the basilar membrane and most other auditory system components Copyright © 2009 Allyn & Bacon

The Ear (continued) Some pathways of the auditory system from one ear to the cortex Copyright © 2009 Allyn & Bacon

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 is laid out according to auditory space, allowing location of sound sources in the world; the shallow layers are laid out retinotopically Copyright © 2009 Allyn & Bacon

Primary and Secondary Auditory Cortex Two or three areas of primary auditory cortex About seven areas of secondary auditory cortex Functional columns (cells of a column respond to the same frequency) Tonotopic organization Secondary areas do not respond well to pure tones and have not been well-researched Copyright © 2009 Allyn & Bacon

Effects of Damage to the Auditory System Lesions of auditory cortex in rats results in few permanent hearing deficits Lesions in monkeys and humans hinder sound localization and pitch discrimination Deafness in humans Total deafness is rare, due to multiple pathways Two kinds: conductive deafness (damage to ossicles) and nerve deafness (damage to cochlea) Partial cochlear damage results in loss of hearing at particular frequencies Copyright © 2009 Allyn & Bacon

Somatosensation: Touch and Pain ` Somatosensory system is three separate and interacting systems: Exteroceptive – external stimuli Proprioceptive – body position Interoceptive – body conditions (e.g., temperature and blood pressure) Copyright © 2009 Allyn & Bacon

Somatosensation: Touch and Pain (continued) Exteroceptive System Touch (mechanical stimuli) Temperature (thermal stimuli) Pain (nociceptive stimuli) Specialized receptors respond to the various stimuli Copyright © 2009 Allyn & Bacon

Somatosensation: Touch and Pain (continued) Cutaneous Receptors Free nerve ending temperature and pain Pacinian corpuscles adapt rapidly, large and deep; onion-like sudden displacements of the skin Merkel’s disks – gradual skin indentation Ruffini endings – gradual skin stretch Copyright © 2009 Allyn & Bacon

Touch and Pain (continued) Four cutaneous receptors that occur in the human skin Copyright © 2009 Allyn & Bacon Figure 7.10. Cutaneous receptors

Somatosensation: Touch and Pain (continued) Cutaneous Receptors We respond to change – when there is no change, no sensation Stereognosis – identifying objects by touch Dermatome – the area of the body innervated by the left and right dorsal roots of a given segment of spinal cord Copyright © 2009 Allyn & Bacon

Two Major Somatosensory Pathways Dorsal-column medial-lemniscus system Mainly touch and proprioception First synapse in the dorsal column nuclei of the medulla Anterolateral system Mainly pain and temperature Synapse upon entering the spinal cord Three tracts – spinothalamic, spinoreticular, spinotectal Copyright © 2009 Allyn & Bacon

medial-lemniscus system Antero-lateral system Dorsal-column medial-lemniscus system Antero-lateral system Two Major Somato- sensory Path- ways (continued) Copyright © 2009 Allyn & Bacon Figure 7.12 , p.173