心理学与生活-第31节

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Other　principles　and　properties　that　are　characteristic　of　all　sensory　systems　include　the　following：　

1。　Limited　Receptivity。　Human　senses　are　structurally　designed　to　respond　to　a　certain　type　of　
energy；　and；　within　that　type　of　energy；　to　a　limited　range　of　output。　All　senses　respond　to　
some　form　of　energy。　Human　vision　responds　to　electromagnetic　radiation　（light）；　from　just　
above　the　ultraviolet　to　just　below　the　infrared　portions　of　the　spectrum。　This　is　known　as　
the　visible　range　of　light。　Audition　responds　to　pressure；　from　about　50　Hz　to　about　15；000　
Hz　in　humans。　The　range　for　dogs　is　much　higher；　up　to　about　100；000　Hz。　The　individual　
ranges　for　all　types　of　receptivity　are　species…specific。　
2。　Specific　Irritability。　Within　a　given　system；　there　are　subsystems　with　specialized　functions。　
In　the　visual　system；　rods　are　more　sensitive　to　shorter　wavelengths　of　light；　cones　are　more　
sensitive　to　longer　wavelengths。　Gustation；　the　sense　of　taste；　relies　on　chemical　energy。　
The　tongue　has　four　basic　types　of　taste　receptors：　sweet；　salty；　bitter；　sour。　Each　of　these　
subsystems　is　sensitive　to　different　chemicals。　
3。　Adaptation。　Sensory　systems　are　designed　such　that　they　will　not　respond　to　steady；　
repetitive；　nonchanging　stimuli；　which　carry　no　further　information。　This　permits　our　
senses　to　respond　over　a　wide　range　of　energy　potential；　such　as　from　dark　to　bright　light。　
Adaptation　permits　resetting　of　the　system　threshold；　over　a　vast　range　of　energy　and　
intensity；　as　needed。　
4。　Contrast。　Sensory　systems　are　designed　to　respond　to　change　relative　to　a　mean　level。　
5。　Threshold；　Saturation；　and　Dynamic　Range。　The　threshold　is　the　minimum　amount　of　energy　
required　for　the　system　to　respond。　Once　above　a　threshold　level；　as　intensity　increases；　so　
does　the　subjective　sensation　of　that　intensity；　across　the　specific　range　to　which　the　system　
responds。　Beyond　a　certain　level；　further　increase　in　physical　intensity　no　longer　produces　
a　subjective　change　in　intensity；　because　the　system　is　saturated。　
6。　Response　Latency。　Every　system　is　a　transducer；　in　that　it　converts　energy　from　one　medium　
to　another　so　that　it　can　be　processed。　This　transduction　process　takes　about　20—30　
milliseconds；　and　about　200—500　milliseconds　following　the　stimulus；　you　bee　aware　
of　the　sensation。　Thus；　we　live　200　milliseconds　in　the　past。　
The　Sensory　System　

In　learning　about　sensation；　it　is　important　for　your　class　to　be　aware　that　we　have　three　different　
types　of　sensory　systems；　each　of　which　performs　different　functions。　

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1。　Exteroceptors。　These　sensory　receptors　take　data　from　the　external　world。　Types　of　
exteroceptors　include　distal　and　proximal　receptors。　Distal　receptors　include　those　
associated　with　vision。　Objects　rarely　make　direct　contact　with　the　eye；　rather　they　are　
discerned　at　a　distance；　with　no　need　for　contact　in　order　to　experience　the　sensation。　
Proximal　receptors　are　associated　with　touch；　taste；　and　possibly　olfaction。　Thermal　
radiation　does　not　always　require　proximity；　you　can　tell　that　the　sun　is　warm　via　your　
distal　receptors–you　do　not　have　to　touch　it。　In　most　instances；　proximal　systems　require　
direct　contact　with　the　stimulus。　
2。　Interoceptors。　These　are　internal　system　monitors；　they　work　to　keep　you　aware　of　the　
internal　working　of　your　body；　such　as　letting　you　know　when　you　are　hungry；　thirsty；　in　
pain；　nauseated；　fatigued；　and　so　on。　
3。　Proprioceptors。　These　receptors　monitor　the　position　of　the　body　or　limbs　relative　to　some　
reference　point。　They　let　you　know　where　you　are　physically　located　in　space。　
Proprioceptors　are　found　in　the　vestibular　system；　where　they　permit　maintenance　of　your　
physical　position；　in　the　pressure　receptors　of　the　skin；　in　the　muscle　stretch　receptors　of　
your　muscles；　and　in　the　joint　movement　receptors　of　your　limbs。　
Auditory　Localization　

We　use　our　ears　to　point　our　eyes　in　the　direction　of　sound…producing　events。　For　this　to　happen；　
the　auditory　system　must　be　able　to　perceive　the　direction　from　which　a　sound　is　originating；　and　
the　system’s　perception　of　space　must　be　integrated　with　the　visual　system’s　perception　of　space。　
Unlike　the　eye；　the　ear　has　no　direct　coding　of　spatial　direction。　Information　about　the　sound’s　
direction　is　perceived　by　paring　the　stimulation　in　one　ear　with　that　in　the　other。　In　this　respect；　
sound　localization　is　much　like　the　visual…depth　cue　of　binocular　disparity。　

There　are　two　basic　sources　of　information　about　sound　ing　from　the　left　or　right；　the　sound　
entering　one　ear　differs　from　that　entering　the　other　in　both　intensity　and　time。　When　a　sound　es　
from　directly　in　front　of　your　head；　its　intensity　is　equal　at　your　two　ears。　In　the　case　of　high…
frequency　sounds　ing　from　the　side；　your　head　creates　a　sound　shadow；　making　the　sound　less　
intense　at　the　ear　farthest　away　from　the　sound　than　at　the　ear　closest　to　the　sound。　It　is　only　for　
high　frequencies　that　there　is　information　about　how　far　to　one　side　or　another　a　sound　is　located。　

The　other　major　source　of　information　about　the　horizontal　direction　of　a　sound　is　the　time　at　which　
it　arrives　at　your　two　ears。　When　a　sound　es　from　directly　in　front　of　your　head；　the　arrival　times　
are　the　same　because　your　two　ears　are　the　same　distance　away　from　the　sound。　However；　when　the　
sound　es　from　the　side；　the　sound　wave　must　travel　farther　to　reach　the　ear　on　the　far　side。　Even　
though　this　extra　distance　takes　only　a　little　extra　time—less　than　one…thousandth　of　a　second—it　is　
enough　to　tell　us　which　side　sound　is　ing　from。　

The　direction　of　sounds　from　left　to　right；　or　right　to　left；　is　probably　the　most　important　part　of　
spatial　hearing；　but　it　is　not　the　only　part。　You　can　also　tell　whether　a　sound　is　ing　from　above　
or　below—the　sound　of　a　jet　streaking　overhead　or　of　an　object　dropped　at　your　feet。　You　are　not　
able　to　perceive　vertical　direction　from　simple　arrival　times　or　intensities；　however。　It　is　the　shape　of　
the　external　ear　that　allows　you　to　perceive　the　vertical　dimension　of　space。　Notice　that　your　ear　is　
asymmetrical。　There　are　many　plex；　sound…reflecting　folds　in　the　pinna　above　the　ear　canal；　and　
few　below　it。　These　differences　in　the　shape　of　the　external　ear　make　subtle　changes　in　the　sound　
wave　that　enters　your　ears；　depending　on　the　vertical　direction　of　the　sound　source。　Somewhere　in　
the　auditory　centers　of　the　brain；　these　differences　are　detected　and　decoded；　allowing　you　to　
perceive　upward　and　downward　directions　of　environmental　sounds。　

We　are　left　with　the　problem　of　perceiving　the　third　dimension　of　depth—how　far　away　the　source　
of　a　sound　is　from　us。　A　sound　that　is　near　is　louder　than　one　that　is　far　away；　so　you　might　think　

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that　intensity　would　provide　all　the　information　you　need　about　the　distance　（or　depth）　of　the　
source　of　a　sound。　Unfortunately；　it　is　not　that　easy。　A　low…intensity　sound　at　the　ear　might　have　
e　from　either　a　loud　sound　far　away　or　a　soft　one　nearby。　This　situation　is　analogous　to　the　
relations　among　retinal　size；　object　distance；　and　object　size　in　visual　perception。　If　the　sound　is　one　
whose　usual　intensity　you　know；　such　as　someone　speaking　in　a　normal　voice　or　the　sound　of　an　
average　car　engine；　you　can　perceive　its　approximate　distance　by　sound　using　intensity　
information。　If　the　sound　is　one　whose　usual　intensity　you　do　not　know；　you　cannot　tell　how　far　
away　it　is　by　hearing　it；　you　have　to　look。　Because　you　can　locate　the　direction　that　the　sound　is　
ing　from　using　your　ears；　you　can　use　them　to　point　your　eyes　in　the　correct　direction；　which　
can　then　do　the　job　of　judging　distance。　

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BIOGRAPHICAL　PROFILES　

Hermann　von　Helmholtz　（1821–1894）　

Hermann　Von　Helmholtz　obtained　his　M。D。　in　Berlin　and　served　subsequently　as　an　Army　surgeon　
for　seven　years。　Following　his　military　service；　he　studied　math　and　physics　and　held　academic　
appointments　over　the　next　30　years　at　Bonn；　Heidelberg；　and　Berlin；　initially　as　a　physiologist；　
later　as　a　physicist。　Helmholtz；　whose　versatility　and　intellectual　brilliance　manifested　itself　in　
various　disciplines；　is　considered　one　of　the　true　giants　in　the　history　of　science。　

Helmholtz’s　prominence　in　physiology　came　chiefly　from　his　discovery　of　the　rate　of　neural　
conduction；　a　finding　that　surprised　many　of　his　contemporaries　who　had　assumed　that　nerve　
impulses　must　travel　at　or　near　the　speed　of　light。　In　addition；　he　invented　the　opthalmoscope　while　
researching　vision；　and　was　involved　in　the　development　of　theories　of　color　vision　and　pitch　
perception　that　remain　influential　today。　His　published　works　include　the　three…volume　series　

Physiological　Optics　（1856—1866）。　

Ernst　Heinrich　Weber　（1795—1879）　

Ernst　Weber　taught　anatomy　and　physiology　at　the　University　of　Leipzig；　Germany；　from　1820　until　
the　end　of　his　career。　He　is　remembered　in　psychology　for　his　studies　of　psychophysical　relations；　
especially　for　the　sensations　of　temperature　and　touch。　Weber　was　the　first　to　investigate　the　two