Hockenbury Discovering Psychology 5th txtbk

108 CHAPTER 3 Sensation and PerceptionCan Humans Track a Scent? Dogsare famous for their ability to tracka scent. Humans? Not so much.However, it turns out that peopleare better trackers than you mightthink. Berkeley scientist Jess Porterand colleagues (2007) embedded along line of chocolate-scented twineinto the ground and then testedwhether human undergraduatescould find and track the scent usingtheir olfactory sense alone. To blockall other sensory cues, the collegestudents wore opaque eye masks,earmuffs, and thick knee pads, elbowpads, and work gloves. Althoughthe human trackers wereable to locate and follow the trail,their average speed was only aboutone inch per second. However, afteronly a few days of practice, thetrackers’ speed doubled, improvingto two inches per second.Although humans are highly sensitive to odors,many animals display even greater sensitivity.Dogs, for example, have about 200 million olfactoryreceptor cells, compared with the approximately10 million receptors that humans have.However, humans are more sensitive to smell thanmost people realize (Shepherd, 2004).In fact, people can train their sense of smell(see photo). In a fascinating study, Wen Li andher colleagues (2006) showed that with repeatedexposure to a particular class of odors (floral orminty), participants improved in their ability todistinguish subtle differences among the differentscents. They also became more sensitive tothe odors. These behavioral changes were accompaniedby changes in the brain: fMRI scansshowed increased activation in the olfactory cortex.The moral? Stop and smell the flowers oftenenough, and you will improve your ability to discriminatea geranium from a marigold.TasteOur sense of taste, or gustation, results from the stimulation of special receptors inthe mouth. The stimuli that produce the sensation of taste are chemical substancesin whatever you eat or drink. These substances are dissolved by saliva, allowing thechemicals to activate the taste buds. Each taste bud contains about 50 receptor cellsthat are specialized for taste.The surface of the tongue is covered with thousands of little bumps with groovesin between (see Figure 3.10). These grooves are lined with the taste buds. TasteFigure 3.10 Taste Buds Contrary to popularbelief, it’s long been known thatthere is no tongue “map” in which differentregions of the tongue are responsiveto different tastes. Instead, responsivenessto the five basic tastes is present in alltongue areas (Chandrashekar & others,2006). (a) The photograph shows the surfaceof the tongue magnified hundreds oftimes. Taste buds are located in thegrooves of the bumps on the surface ofthe tongue. (b) Embedded in the surfaceof the tongue are thousands of taste buds,the sensory receptor organs for taste. Eachtaste bud contains an average of 50 tastereceptor cells. When activated, the tastereceptor cells send messages to adjoiningsensory neurons, which relay the infor -mation to the brain. Taste buds, like theolfactory neurons, are constantly beingreplaced. The life expectancy of a particulartaste bud is only about 10 days.(b)(a)Taste budsBump on thesurface of thetongue