Hockenbury Discovering Psychology 5th txtbk

90 CHAPTER 3 Sensation and PerceptionSensationPerceptionIt smells like a lily.Energy from an environmentalstimulus activates specializedreceptor cells in the sense organ.Figure 3.1 The Basic Steps of Sensationand Perceptionabsolute thresholdThe smallest possible strength of a stimulusthat can be detected half the time.subliminal perceptionThe detection of stimuli that are below thethreshold of conscious awareness; nonconsciousperception.mere exposure effectThe finding that repeated exposure to astimulus increases a person’s preference forthat stimulus.Coded neural messages are sentalong a specific sensory pathwayto the brain.These neural messages aredecoded and interpreted inthe brain as a meaningfulperception.atmosphere and passing through your body. However, sensory receptors are sohighly specialized that they are sensitive only to very specific types of energy(which is lucky, or you might be seeing Gilligan’s Island reruns in your brain rightnow). So, for any type of stimulation to be sensed, the stimulus energy must firstbe in a form that can be detected by our sensory receptor cells. Otherwise, transductioncannot occur.Sensory ThresholdsAlong with being specialized as to the types of energy that can be detected, our sensesare specialized in other ways as well. We do not have an infinite capacity to detect all levelsof energy. To be sensed, a stimulus must first be strong enough to be detected—loudenough to be heard, concentrated enough to be smelled, bright enough to be seen. Thepoint at which a stimulus is strong enough to be detected because it activates a sensoryTable 3.1Absolute ThresholdsSense Absolute ThresholdVision A candle flame seen from30 miles away on a clear,dark nightHearing The tick of a watch at 20 feetTaste One teaspoon of sugar in twogallons of waterSmell One drop of perfume throughouta three-room apartmentTouch A bee’s wing falling on yourcheek from a height of abouthalf an inchPsychologist Eugene Galanter (1962)provided these classic examples of theabsolute thresholds for our senses. In eachcase, people are able to sense these faintstimuli at least half the time.receptor cell is called a threshold. There aretwo general kinds of sensory thresholds foreach sense—the absolute threshold and thedifference threshold.The absolute threshold refers to thesmallest possible strength of a stimulus thatcan be detected half the time. Why just halfthe time? It turns out that the minimumlevel of stimulation that can be detectedvaries from person to person and from trialto trial. Because of this human variability,researchers have arbitrarily set the limit asthe minimum level of stimulation that canbe detected half the time. Under ideal conditions(which rarely occur in normal dailylife), our sensory abilities are far more sensitivethan you might think (see Table 3.1).Can stimuli that are below the absolutethreshold affect us? We discuss this questionin the Science Versus Pseudosciencebox, “Subliminal Perception.”