Mechanisms of Perception: Hearing, Touch, Smell, Taste, and Attention (164-190)
Principles of Sensory System Organization
- Exteroceptive sensory systems contain the auditory, somatosensory, olfactory, and gustatory systems. The
primary sensory cortex of a system is the area of sensory cortex that receives most of its input directly from the
thalamic relay of nuclei of that system. The secondary sensory cortex of a system compromises the areas of
sensory cortex that receive most of their input from the primary sensory cortex of that system or from other areas
of the secondary sensory cortex of the same system. Association cortex in any area of cortex that receives input
from more than one sensory system.
- Sensory systems are characterized by hierachical organization. Receptors
Thalamic Relay Nuclei
Secondary Sensory Cortex
Association Cortex. Sensation is the process of detecting the
presence of stimuli, and perception is the higher-order process of integrating, recognizing, and interpreting
complete patterns of sensations. Functional segregation characterizes the organization of sensory systems. A
serial system is a system in which information flows among the components over just one pathway, like a string
through a strand of beads. Sensory systems are thought to be parallel systems, systems in which information
flows through the components over multiple pathways. Parallel systems feature parallel processing, the
simultaneous analysis of a signal in different ways by the multiple parallel pathways of a neural network.
Sensory systems are characterized by a division of labor: multiple specialized areas, at multiple levels, are
interconnected by multiple parallel pathways.
- Sounds are vibrations of air molecules that stimulate the auditory system; humans hear only those molecular
vibrations between about 20 and 20,000 hertz. The amplitude, frequency, and complexity of the molecular
vibrations are most closely linked to perceptions of loudness, pitch, and timbre. Pure tones (sine wave vibrations)
exist only in laboratories and sound-recording studios; in real life sound is always associated with complex
patterns of vibrations. Fourier analysis is the mathematical procedure for breaking down complex waves into
their component sine waves. For any pure tone there is a close relationship between the frequency of the tone and
its perceived pitch, however the relation between the frequencies that make up natural sounds and their perceived
pitch is complex. The pitch of such sounds is related to their fundamental frequency, the highest frequency of
which the various component frequencies of a sound are multiples. The pitch of a complex sound may not be
directly related to the frequency of any of the sound’s components, this is known as the missing fundamental.
- Sound waves travel from the outer ear down the auditory canal and cause the tympanic membrane (eardrum) to