Sensation occurs when sensory receptors detect sensory stimuli. Perception involves the organization, interpretation, and conscious experience of those sensations. All sensory systems have both absolute and difference thresholds, which refer to the
minimum amount of stimulus energy or the minimum amount of difference in stimulus energy required to be detected about 50% of the time, respectively. Sensory adaptation, selective attention, and signal detection theory can help explain what is perceived and what is not. In addition, our perceptions are affected by a number of factors, including beliefs, values, prejudices, culture, and life experiences. Both light and sound can be described in terms of wave forms with physical characteristics like amplitude, wavelength, and timbre. Wavelength and frequency are inversely related so that longer waves have lower frequencies, and shorter waves have higher frequencies. In the visual system, a light wave’s wavelength is generally associated with color, and its amplitude is associated with brightness.
In the auditory system, a sound’s frequency is associated with pitch, and its amplitude is associated with loudness. Light waves cross the cornea and enter the eye at the pupil. The eye’s lens focuses this light so that the image is focused on a region of the retina known as the fovea. The fovea contains cones that possess high levels
of visual acuity and operate best in bright light conditions. Rods are located throughout the retina and operate best under dim light conditions. Visual information leaves the eye via the optic nerve. Information from each visual field is sent to the opposite side of the brain at the optic chiasm. Visual information then moves through a number of brain sites before reaching the occipital lobe, where it is processed.Sensation versus Perception
Waves and Wavelengths
Vision
Two theories explain color perception. The trichromatic theory asserts that three distinct cone groups are tuned to slightly different wavelengths of light, and it is the combination of activity across these cone types that results in our perception of all the colors we see. The opponent-process theory of color vision asserts that color is processed in opponent pairs and accounts for the interesting phenomenon of a negative afterimage. We perceive depth through a combination of monocular and binocular depth cues.
Gestalt Principles of Perception
Gestalt theorists have been incredibly influential in the areas of sensation and perception. Gestalt principles such as figure-ground relationship, grouping by proximity or similarity, the law of good continuation, and closure are all used to help explain how we organize sensory information. Our perceptions are not infallible, and they can be influenced by bias, prejudice, and other factors.
Hearing and the Other Senses
Sound waves are funneled into the auditory canal and cause vibrations of the eardrum; these vibrations move the ossicles. As the ossicles move, the stapes presses against the oval window of the cochlea, which causes fluid inside the cochlea to move. As a result, hair cells embedded in the basilar membrane become enlarged, which sends neural impulses to the brain via the auditory nerve.
Pitch perception and sound localization are important aspects of hearing. Our ability to perceive pitch relies on both the firing rate of the hair cells in the basilar membrane as well as their location within the membrane. In terms of sound localization, both monaural and binaural cues are used to locate where sounds originate in our environment.
Individuals can be born deaf, or they can develop deafness as a result of age, genetic predisposition, and/or environmental causes. Hearing loss that results from a failure of the vibration of the eardrum or the resultant movement of the ossicles is called conductive hearing loss. Hearing loss that involves a failure of the transmission of auditory nerve impulses to the brain is called sensorineural hearing loss.
Taste (gustation) and smell (olfaction) are chemical senses that employ receptors on the tongue and in the nose that bind directly with taste and odor molecules in order to transmit information to the brain for processing. Our ability to perceive touch, temperature, and pain is mediated by a number of receptors and free nerve endings that are distributed throughout the skin and various tissues of the body. The vestibular sense helps us maintain a sense of balance through the response of hair cells in the utricle, saccule, and semi-circular canals that respond to changes in head position and gravity. Our proprioceptive and kinesthetic systems provide information about body position and body movement through receptors that detect stretch and tension in the muscles, joints, tendons, and skin of the body.
Key Terms
absolute thresholdminimum amount of stimulus energy that must be present for the stimulus to be detected 50% of the timeafterimagecontinuation of a visual sensation after removal of the stimulusamplitudeheight of a wavebasilar membranethin strip of tissue within the cochlea that contains the hair cells which serve as the sensory receptors for the auditory systembinaural cuetwo-eared cue to localize soundbinocular cuecue that relies on the use of both eyesbinocular disparityslightly different view of the world that each eye receives blind spotpoint where we cannot respond to visual information in that portion of the visual fieldbottom-up processingsystem in which perceptions are built from sensory inputclosureorganizing our perceptions into complete objects rather than as a series of partscochlea fluid-filled, snail-shaped structure that contains the sensory receptor cells of the auditory systemcochlear implantelectronic device that consists of a microphone, a speech processor, and an electrode array to directly stimulate the auditory nerve to transmit information to the brainconductive hearing lossfailure in the vibration of the eardrum and/or movement of the ossiclesconespecialized photoreceptor that works best in bright light conditions and detects colorcongenital deafnessdeafness from birthcongenital insensitivity to pain (congenital analgesia)genetic disorder that results in the inability to experience paincorneatransparent covering over the eyedeafnesspartial or complete inability to heardecibel (dB)logarithmic unit of sound intensitydepth perceptionability to perceive depthelectromagnetic spectrumall the electromagnetic radiation that occurs in our environmentfigure-ground relationshipsegmenting our visual world into figure and groundfoveasmall indentation in the retina that contains cones frequencynumber of waves that pass a given point in a given time periodGestalt psychologyfield of psychology based on the idea that the whole is different from the sum of its partsgood continuation(also, continuity) we are more likely to perceive continuous, smooth flowing lines rather than jagged, broken lineshair cellauditory receptor cell of the inner earhertz (Hz)cycles per second; measure of frequencyinattentional blindnessfailure to notice something that is completely visible because of a lack of attentionincusmiddle ear ossicle; also known as the anvilinflammatory painsignal that some type of tissue damage has occurredinteraural level differencesound coming from one side of the body is more intense at the closest ear because of the attenuation of the sound wave as it passes through the headinteraural timing differencesmall difference in the time at which a given sound wave arrives at each eaririscolored portion of the eyejust noticeable differencedifference in stimuli required to detect a difference between the stimulikinesthesiaperception of the body’s movement through spacelenscurved, transparent structure that provides additional focus for light entering the eyelinear perspectiveperceive depth in an image when two parallel lines seem to convergemalleusmiddle ear ossicle; also known as the hammerMeissner’s corpuscletouch receptor that responds to pressure and lower frequency vibrationsMénière’s diseaseresults in a degeneration of inner ear structures that can lead to hearing loss, tinnitus, vertigo, and an increase in pressure within the inner earMerkel’s disk touch receptor that responds to light touchmonaural cueone-eared cue to localize soundmonocular cuecue that requires only one eyeneuropathic painpain from damage to neurons of either the peripheral or central nervous systemnociceptionsensory signal indicating potential harm and maybe painolfactory bulbbulb-like structure at the tip of the frontal lobe, where the olfactory nerves beginolfactory receptorsensory cell for the olfactory systemopponent-process theory of color perceptioncolor is coded in opponent pairs: black-white, yellow-blue, and red-greenoptic chiasmX-shaped structure that sits just below the brain’s ventral surface; represents the merging of the optic nerves from the two eyes and the separation of information from the two sides of the visual field to the opposite side of the brainoptic nervecarries visual information from the retina to the brainPacinian corpuscletouch receptor that detects transient pressure and higher frequency vibrationspattern perceptionability to discriminate among different figures and shapespeak(also, crest) highest point of a waveperceptionway that sensory information is interpreted and consciously experiencedperceptual hypothesiseducated guess used to interpret sensory informationpheromonechemical message sent by another individual photoreceptorlight-detecting cellpinnavisible part of the ear that protrudes from the headpitchperception of a sound’s frequencyplace theory of pitch perceptiondifferent portions of the basilar membrane are sensitive to sounds of different frequenciesprinciple of closureorganize perceptions into complete objects rather than as a series of partsproprioceptionperception of body positionproximitythings that are close to one another tend to be grouped togetherpupilsmall opening in the eye through which light passesretinalight-sensitive lining of the eyerodspecialized photoreceptor that works well in low light conditionsRuffini corpuscletouch receptor that detects stretchsensationwhat happens when sensory information is detected by a sensory receptorsensorineural hearing lossfailure to transmit neural signals from the cochlea to the brainsensory adaptationnot perceiving stimuli that remain relatively constant over prolonged periods of time signal detection theorychange in stimulus detection as a function of current mental statesimilaritythings that are alike tend to be grouped togetherstapesmiddle ear ossicle; also known as the stirrupsubliminal messagemessage presented below the threshold of conscious awarenesstaste budgrouping of taste receptor cells with hair-like extensions that protrude into the central pore of the taste budtemporal theory of pitch perceptionsound’s frequency is coded by the activity level of a sensory neuronthermoceptiontemperature perceptiontimbresound’s puritytop-down processinginterpretation of sensations is influenced by available knowledge, experiences, and thoughtstransductionconversion from sensory stimulus energy to action potentialtrichromatic theory of color perceptioncolor vision is mediated by the activity across the three groups of conestroughlowest point of a wavetympanic membraneeardrumumamitaste for monosodium glutamatevertigospinning sensationvestibular sensecontributes to our ability to maintain balance and body posturevisible spectrumportion of the electromagnetic spectrum that we can seewavelengthlength of a wave from one peak to the next peak