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Sensation versus PerceptionLEARNING OBJECTIVESBy the end of this section, you will be able to:Distinguish between sensation and perceptionDescribe the concepts of absolute threshold and difference thresholdDiscuss the roles attention, motivation, and sensory adaptation play in perceptionSENSATIONWhat does it mean to sense something? Sensory receptors are specialized neurons that respond to specifictypes of stimuli. When sensory information is detected by a sensory receptor, sensation has occurred. Forexample, light that enters the eye causes chemical changes in cells that line the back of the eye. These cellsrelay messages, in the form of action potentials (as you learned when studying biopsychology), to the centralnervous system. The conversion from sensory stimulus energy to action potential is known as transduction.You have probably known since elementary school that we have five senses: vision, hearing (audition), smell(olfaction), taste (gustation), and touch (somatosensation). It turns out that this notion of five senses isoversimplified. We also have sensory systems that provide information about balance (the vestibular sense),body position and movement (proprioception and kinesthesia), pain (nociception), and temperature(thermoception).The sensitivity of a given sensory system to the relevant stimuli can be expressed as an absolutethreshold. Absolute threshold refers to the minimum amount of stimulus energy that must be present for thestimulus to be detected 50% of the time. Another way to think about this is by asking how dim can a light be orhow soft can a sound be and still be detected half of the time. The sensitivity of our sensory receptors can bequite amazing. It has been estimated that on a clear night, the most sensitive sensory cells in the back of theeye can detect a candle flame 30 miles away (Okawa & Sampath, 2007). Under quiet conditions, the hair cells(the receptor cells of the inner ear) can detect the tick of a clock 20 feet away (Galanter, 1962).It is also possible for us to get messages that are presented below the threshold for conscious awareness—these are called subliminal messages. A stimulus reaches a physiological threshold when it is strong enough toexcite sensory receptors and send nerve impulses to the brain: This is an absolute threshold. A message belowthat threshold is said to be subliminal: We receive it, but we are not consciously aware of it. Over the yearsthere has been a great deal of speculation about the use of subliminal messages in advertising, rock music,and self-help audio programs. Research evidence shows that in laboratory settings, people can process andrespond to information outside of awareness. But this does not mean that we obey these messages likezombies; in fact, hidden messages have little effect on behavior outside the laboratory (Kunst-Wilson & Zajonc,1980; Rensink, 2004; Nelson, 2008; Radel, Sarrazin, Legrain, & Gobancé, 2009; Loersch, Durso, & Petty,2013).