Scaling Methods Mov ing beyond absolute thresholds a nd difference thresh olds, s uppose we '""' anted to kn ow about tile magni tude of your experiences. Though that might seem like an odd ques tion , it tunlS out to be a nswerable. We could give you a knob to adjust so that you could set the second light to appear twice as bright as the first, and you could do it We don 't need to give the observers a light to adjust.
A s urprising! For exa mple, we could give observers a series of s ugar solutions and as k the m to assign numbers to each sample. More typically, we might begin the experiment by presenting one solution at a n inte nnediate level and telling the taste r to label this level as a specific val ue, for insta nce. All of the responses should then be scaled sensibly above or below this stand a rd of H you d o this for s ugar solutions, you ,viU get d a ta tk1t look like the blue "sweetness" line in Figure 1.
The lines on this graph represent data from magnitude estimation QXpel'"iITIQflts using electric shocks o f diffgrent cutnaots, lines o f diff9t"ent lengths. Th9 90 80 exponents that describe these lings are 3. Fer exponents greater than 1, such as for electric shock, Fechner' s law does not hcid , 70 and Stevens' power law must be used instead.
Harva rd psychologis t S. Stevens , in vented magni tude estimation. H e, his s htdents, and successo rs. Even tho ugh observers were asked to assign num bers to priva te experien ce, the resul ts were m derly and lawful. Thzit rebtionship betv..
So 1 for ex. That would be an exponent of 2. If the exponent is less than 1, this mea ns that the sensat ion grows less rapidly than the s timulus.
S is w ha t Fechner's law and Weber's law would predict. Suppose you have some lit ca ndles and you li ght 10 more. In fact, the exponen t for brightness is about0. The exponent for swee tness is about0. Properties like length h ave e.. Stevens and Galanter, Note tha t th is relations hip is true over only a m oderate range of sizes. In the painful case of e lectric sh ock, the pain grows wi th f3. S Stevens, Ca rton, and Shickman, , so a 4-fo.
Jn particular, Fechner 's law assumes tha t all JNDs are perceptually equi valent. This ability allows Insight Into sensay differenoes. For example. Supertasters atso tend to experience more Intense oral burn and cral tc:uci1 sensatlcn s. A use ful varian t of the scaling method can s h ow us tha t different individ uals can live in different sensory worlds, even if they are exposed to the same stimuli.
The me thod is cross-modality matching Q. Stevens, In cross-modality matching, a n observer adjusts a s timulus of one sort to m atd1 the perceived magnitude of a s timulus o f a completely different sort. For examp le, we might ask a listener to adjust the brighh1ess of a light until it matches the loudne Again, though the task might sound odd, people c.. Not so w hen it comes to the sense of taste.
There is a molecule cal led p ropylthiouracil PROP that some people experience as Supa-tastersvery bitter, '"'hil e others expe rie nce it as almos t tu. S till oth ers fall in between. This relationship can be examined formally with cross-modali ty matching Marks et al. If observers ore asked to match the bitterness of PROP to oth er. Some people- we'll call them nontasters-match the taste of PROP to very weak sensation s like the solUld of a watch or a w hisper.
Medium tasters matdl PROP to weaker stimuli, such as the smell of frying bacon o r the pain of a mild headache Bartoshuk, Fast, and Snyder, S wide implications for our food preferences and, conseciuently, for health. Matching sensations l. Th9 perceiv9d intensities of a varigty o f everyday SQnsatb ns arg shown ori the right. Data from Fast, Onsss du. In this book, in addition to covering most of w hat was then known about physiology,lvli.
The central idea of this doctrine is that Vv""e cannot be directly aware of the world itself, and we are only 3ware of the activity in our nerves.
Further, wha t is most impor t. For exa mp le, we exp erience vision because the op tic n erve leading fr om the eye to the brain is s timulated, but it d oes not ma tter whethe r light, or.
To prove to yourself that this is true, close yom eyes and press very gently on the outside com er of one eye through the lid. This works better in a darkened room. Desp ite the lack of s timulation by light, yo ur brain interp rets the input from y01rr optic nerve as in for min g you about some thing visual. The cranial nerves leading into and out of the skull illus trate the d octrine of specific nerve energies Figure 1.
Cf b oth. After Breedlove and Watson. VIL F. The cra nial nerves o:u e d edicated m ainly to sensory a. Crnnial nerves are labeled both by names and by Roman numerals thilt roughly correspond to the order of their loc. The axons of the olfactory sensoiy neurcns bundle together after passing throu;ih the crlbrlform plate to fam the dfactory nerve, which ducts impulses fran the olfactory eplthella In the nose to the olfactory bulb.
Activated neurons provcke Increase:! You might use behavioral methods to determine the nature of a particular perceptual but s uch methods mjght take hollfS and htrndreds or thousands of tria ls. You might do yet an o ther version of the task, specialized for the de mands of BEG recording. By means of these "con vergin g operations," you co uld build up quite a d eta iled picture of what perceives and how her brain gives rise to those perceptions. Now tha t yo u've compl eted this brief tour of the methods of the trade, you.
We h ope you enjoy the journey. Much of the light energy will have been lost in space or the atmosphere, becc1 use of absorption and scatterin g. In addition, a good deal of light becomes lost in the eyeball, so only about half of the that arrives at the cornea actually reach es the retin.. The role of the reti na is to detect light and "te ll the brain about aspects of lig ht that are rela ted to objects in the world" Oys ter, Focusing Ught onto the Retina To foc us a dis tant star on the retina, the refractive power of the four optic components of the eye mus t be perfectly matched to the length of the eyeball.
This perfect matd1, known as emmetropia, i s illus trated in Figure 2. The average eyeba ll is abo ut 24 millimeters mm lon g a nd h.. We'll explain what accommodation means in a bit. Jeous humor The watery fluid In the anter1or chamber of the f1' Ye Is focused ln frcnt of the retina and distant objects cannot be soon sharply. Blly the cornea. See the text for details. Refractive errors occur when the eyeball is too long or too short relative to the power of the optic components.
If the eyeba ll is too long for the optics Ftgure 2. Th is condition is called myopia or "nearsightedness". Myopia can be corrected with negative mi nus lenses, wh ich di verge the rays of starlight before they enter the eye Figure 2. If the hyperopia is not too severe, a youn g hyperope ca n compensate by accommoda ting, the reby increasing the power of the eye.
If accommodation foils to correct the hyperopia, the star's image ,,,,. Hyperopia can be corrected vdth positive plus le nses, w h ich con verge the rays of s ta rli ght before they en ter the eye. On average, the adult human eye is 24 mm long, abo ut the diameter of a quarter. However, eyeballs can be quite a bit longer or s horter and s till be ernmetropk because eyes generally grow to ma tch the pmver of the optic components we're born with.
Most newborns. With astig matis m, verti ca l lines might be focused sli ghtly in front of the retirn::i1 w hil e horizontal l. If you h. Len ses that have h-vo focal poin ts that is, lenses that provide different amounts of focusing power in the horizontal and vertical planes can correct astigmatism.
So far, we've considered the image of a distant object. Remember that refraction light bending is n ecessary to foc us light rays. Because the cornea is highly curved and has a higher refractive index tha n air L versus 1 1 it for ms the most p owerful refractive s urface in the eye. The aqueous and "itreous humors also help refract light. However, the refractive power of each of these three structures is fi. This job is performed by the lens, which can alter the refracti ve power by cha nging its s hape-a process called accommodation.
When the ciliary muscle is relaxed, the zonules c'. This contracti on red uces the tension on th e zonules and enables the lens to bulge. The fatter the lens is, the m ore p ovver it has. Tais of accommcdatlon, which makes It near objects. What the Doctor Saw transck. The transduction of light energy into neural energy begins in the back. When photoreceptors sense light, they can s timulate neurons in the intermediate layers, including bipolar cells, horizontal cells, and am acrine cells.
Before we describe the function of these layers, we sho uld a ddress an obvious question regarding the structure of the retina see Figure 2. This ar ran gement requires ligh t to pass throu gh the gang li on, horizon tal, and amacrin e cells before making contact with the photoreceptors.
O n ce we see th at the photo-receptors mus t be next to both the pig1r1ent epithelium and the o ther neumns, the layering order makes much m ore sense. Retinal Geography and Function The retin a con tains roughly million photoreceptors. These are the neurons that capture lig ht and initiate the ac t o f seeing by producing chemical sign als.
The hmn an retina contains at least two types of photoreceptors: rods and cones. Because retinas have both rods and cones, they are cons idered to be duplex retinas. Some animals, su ch as rats and owls, have n10s tl y rod retinas; others e. Huma ns have many m ore rods about 90 million than cones about million , a nd the two types of cell s ha ve very different geographic distributions on the retina Figure 2. Rods a re completely absent from the center of the fovea, and their d en sity increases to a peak a t about 20 d egreES and then declines again.
The cones a re most con centrated in the center of the fovea, an d their dens ity drops off drama ticaJly wi th retin al eccentricity d i. The fo vea is the 11pit" in the inne r retina that is specialized for seeing fine detail.
As the photographs of photoreceptors a t different eccentricities in Figure 2. How big is 1 degree? Table 2. Most important for us, the fovea has hi gh acuity an d we use it to identi fy objects, to read, and to inspect fine d e tail. O n the o ther hand , we use the periphery w hen d etecting and localizing stimuli tha t we aren't lookfrlg at directly e.
TI1e cones become larger and more sparse away from the foveal center, and the s mall ce lls that appem outside the fovea e. Having an area at the center of the fovea with n o rods means th at under dim illumina tion the central 1 degree or so around the fovea is e ffectively blind!
Ind eed , practiced. We '"rill revisit ph otopic and scotopk vision again in 01ap te r 5. Rods and cones d iffer fun ctio n. Uy in another important way. Because all rods h ave the same type of photo pig ment, they ca nno t signal differences in color. Ead1 con e, on th e o ther hand , has one of three differentpho topig ments that differ in the wavele ngths at w hich they absorb light m ost efficientl y. Therefore, cones can signal information about wavelen gth, and thus they provide the basis for o ur co lor vision.
Retinal Information Processing The retina contains fi ve major classes of ne urons: photoreceptors, h orizontal cells, bipolar cells, amacrine cells, and ganglion cells mentioned in the prev ious section see Figure 2. Let's take a cl oser look at the fonctions of each of these cell types. See Web Activity 2. Molecules called visual pigments are m ade in the inner segment whid1 is like a little factory, filled with mitochondria and stored in the outer segment, w here they are incorporated into the membran e.
The chromophore is the part of the molecule respons ible for its color, and it selectively absorbs specific vvavelengths of light. The chromophme, known as retin. The opsin and ch romophore are co nnected. Each photoreceptor has only one of the four types of vis ual pigments fol. Each cone has one of the other th ree pigments-which respond to lon g, med.
Recen t evidence su gges ts that there may be a third type of pho toreceptor--one that ''lives'' a mong the ganglion cells and that is involved in adjusting o ur bi ological rhytlu11s to m. These photorecep tors are sensi ti ve to the ambient light level and con tain the photopigment melanopsln, and they send their signals to the An evaluation version of novaPDF was used to create this PDF file.
The ablllty to PffOOMl via the sense organs. Extreme rooponsMiness to radlatbn, especially to Ilg ht of a spedl c wavelength. The ability to respond to transmitted elgnals. ON bipolar cell A bipolar c ell that responds to an lnorease In light c aptured by the cones. OFF bipolar cell A bipolar cell that responds to a decrease In light captured by the cones. P ganglion cell A small ganglion cell that recewes excitatory Input elngle midget bipolar cells In the central retina am feeds the paivocellular 1 : 'fer of the lateral genlculate nuleus.
M ganglion cell A ganglion cell resembling a little umbrella that reOOvoo excitatory Input from diffuse bipolar cells and feeds the magno- cellular layer of the lateral genlculate nuleus.
ShO"Ml are ganglion calls in sQCtion. After Oyst er, Other gang lio n cell types, known as konlocellularcells, project to koniocellular layers in the LG N. Some of these, wi th input from S-cones, may be part of a ''primordial '' blue-yellow p athwc1y seeChn pter 5 , w lUle yet other gan glion cells that p roject to the konlocellular layers a re thou ght to corresp o nd to "n onblu e 11 ko n.
Gangli on cells fire acti on p o ten tia ls sp ontaneo usly, at il bout on e spike p er second, e ven in the absen ce o f vis uaJ s timul ation.
The recep tive fie ld is the region on the retina in which vis ual s timuli influence the neu ron' s fir ing rate. Th is influence can be eithe r exci ta tory, increasi n g the gan g lion's firing ra te, o r inhibitory, d ecreasin g the gang lio n's firing rate. This layer Is knoW11 as the konlocellular layer.
But it w as Stephen Kuffl er vd10 first m apped out the receptive fields of individual retinal gan glion cells in the cat, using s mall spo ts of light Kuffler, Flgure 2. Kuffler 1s expe rimen ts a re sllnulated in Web Ac tivity 2. Let's conside r Fig ure 2. It is in teres ting tha t tuming the light off in th. In each image on the left, the small white circle illustrates thEi region o n thQ r9tina whera thQ rc;itinal ganglion CQll increased its firin g rate whoo the spot small yellow circle was turn9d on.
The largg gray c irc le illus trates the region on the retina where. The pbts on the right illustrate the spikes fired by the retlpal ganglion C In each lmag4': on the left, the large Wille c irc le Illustrates thQ region on th9 retina v.
See Web Essay 2. At present, there are no effective cures top-event the progressive degeneration of the photoreceptors that ocour in these diseases. For patients with AMD this may lead to an lnablllty to read or recognize faces. Fcr patients with long-standing RR this leads nevltably to lrreversltle blindness. Fortunately, there are several excltst-receptor reurons and their connections are largely Intact. One such approach is to substitute an electronic prosthesis an artlficlBI devloo to repace or augment a missing or Impaired part of the bodYl Into the retina.
Typi cally the prosthesis uses a camera to convert light Into energy; an array of electrodes Implanted in the retina generates an e-. Unfortunately, v. Jn, , allowing only perooptlon of spots of light end very high-contrast edges. Another approach that has had some earty success In animal models Is to use gere therapy to express Nght-actlvated channels lsmus A mlsaJlgnment of the two eyee such that a single object In space Is Imaged on the fovea of one eye and on a nonfoveal area of the other aye, anlsometropia A oondttlm In which the two"""" have d ifferent refractive errcrs e.
But when tested ag ain 1 month later, acuity in her left eye had already begun to catch up vvith the acuity in her right "fe. In fact. For example, in much of the third world , because of poverty, children b orn w tth congenital catarac ts often in both "f9S go untreated and grow up essentially blind. According t o the Wortd Health Organization , India Is home to the largest population of blird children in the wor1d. These studies are Just be;Jlnning to provide important new Insights Into brain pl asticity.
Congenital cataracts are not the mly cause of amb lyopla. These fonns of amblycpla are typically less severe , and often they have a later onset than congenital cataracts. The standard clinical treatm ent fo r aml:Jyop a, for over years, 11as been to patch the good aye and ''l crce" the ambtyopic eye to work. This treatment is ordinarily perchildren typically younger than 8 years.
However, formed only in several recent studies suggest that there may be hope for recovery of visio n in okJer children. In this cha pter we followed the path of image p rocessing from the eyeball to the brain.
Neurons in the cerebral cortex translate the array of activity signaled by retinal ganglio n cells into the beginnings of forms and patterns. The primary visual cortex is organized into thousands of tiny computers, each responsible for determini ng the orienta tion, w idth, color, and o ther characteri stics o f the s tripes in one small portion o f the visual field. In Chapter 4 we will continue this story by seeing how other parts of the brain combine the outputs from these minicomputers to produce a coherent representation.
Perha ps the mos t important feature of image processing is the remarkable transformation o f info rmation from the circular recep tive fields o f retinal ganglion cells to the elongated receptive fields of the cortex.
Cortical neurons are highly selective along a num ber of dimensions, including stimulus orientation,.
Neu rons with s imilar preferences are often arranged in columns in prim ary visual cortex. Seledi ve adaptation provides a powerful, n oninvasive tool for learning about s timulus speci ficity in human vision. The htunan visual cortex contains pattern an.. Normal v isual d evelopment requires normal visual experience.
Refer to the Sensation and Perception Companirn Website sltes. Perceiving and Recognizing Objects from the eyes into the brain. Of course, when you look at the world, you d o not see an a rray of bars and g ratingsi you see co herent o bjects and extended surfa ces.
Moreover, you recognize speci fic o bjects even H they are odd objects, as in Figure 4. C hapter 4 continues our journey through the visua l system and considers how that visuTI as the what patlnvay. This p athway appears to be the locus for the explici t acts of object recogniti o n tha t a re of particular imp ortance in this chapter U ngerlei der and Mishkin, However, tho ugh it is a useful organizing principle, one sho uld n ot becom e too addicted to this whnt an d where distinction.
Early evidence for a relati onship bernreen the tempo ral lobe and object recogniti on came fro m s tudi es in w h. Humans have comparable visual areas Figura 3. Each abbreviatio n refers to a. Visual cortical i::rocesslng can be divided into two broad stn'.
O ne, heading for the parietal lcbe, can be thought of as being lntbfested in whGra things are. It is probably a bit extreme to imagine that this is the work of a single neuron in the lT cortex, and more recen t work has cas t d oubt on the idea tha t IT cells respond to an object independent of its position in the visual field DiCa rloa nd Maunsell, Nevertheless, it does seem clear tha t cells in tha t part of the brain are critically involved in object recognition.
This is important because those IT cells need to learn th eir receptive-field properties. In this case, too cell responds vigorously to a rnooksy faca and to som e othgr stimu fi that seQITI related. After Gross. A fter training monkeys to recognize novel objects, these researchers found IT neurons that responded with high firing rates to those objects, hut only w hen the objects were seen from viewpoints similar to those from which they had been leanled.
Human cortex has areas that appear to be the equivalent of monkey IT cortex the anatomy of human and macaque monkey brains is not identical, so we talk about homologous regions.
One of the more amazing demonstrations of this fact comes from a 2 5 study by Quiroga et al. They made recordings from single cells in the temporal lobe of human observers. Normally we do not put electrodes into the human hrain, but these observers were patients being prepared for brain surgery to treat epilepsy.
Implanting electrodes was part of the treatment plan, and recording visual responses' from these cells involved An evaluation version of novaPDF was used to create this PDF file. This oell responded to pictures of the actress JEf'lnifer Alliston. As Figure 4. Other cells had preferen ces for other people, like former Presid ent Bill C linto n. One ce ll responded to the Sydney Opera Ho use; an othe r, to the Eiffel Tower and the l ea ning Tower of Pisa but not to other londmar ks Quiroga et al.
Conveniently, as s how n in Figure 4. T1'1e visual system has m an y differen t problems to solve-like the problem of face proces. Like K. Som etimes these a gn osias can be quite s p eci fi c. Prosop agno. There are other interes ting subdivi s ions of agnosia as welt s uch as the ability to recognize anirnate objects e.
The implicati ons of specific agnosi:as in s p ecific pa tients sh ould no t be taken too far. While 3reas s pecia lized for faces o r place.
Some p rocessing that lead s to the catego ri zation of objects and scenes can be very fas t. Electri cal ac ti vity from the brain can be recorde d froin e lectrodes placed on the scalp. If we flash a p ic ture to an observer and a s k whether it contains a n animal, we ca n record a s ig na l in the observer that reliably differe ntia tes an im al from nonanimal scenes w ithin milli seconds ms from the onset of the s timulus Fize, and tvlar:lot, That's fas t en ough to mean that there cannot be a lo t of feed back fr om higher visual or m emory processes, suggesting that it must be possible to do sorne rou gh object recognition on the basis of the first wave of ac tivity as it m oves, cell by cel l, synapse by syna pse, from retina to stria te cortex to extras tri Tha t feed-forward process mus t be able to gen erate an "an.
To summari ze, two path,-vaysernerge from visual cortex. The -whnt pathway m oves through a s uccession of stages, building a rep resen ta tion of your g randm othe r or the Eiffel Tower out of the very. That' s a but d on 't be lu1led into thinking we fully unders tand the p rocess of object recognition si mply because we ha ve som e n oti on of the ne tual pa th ways involved. It is a really difficult p roblem, and in the rest of the ch apter we will illus trate wh y this problem is ha rd and how the visu al system.
The imag e may contain som e o ther things as well, but the chief object of in teres t is the house. It is p retty clear that Figure 4. Figures a re two more pictures of h ouses.
It is quite d ear tha t Figure Bc is the sam e ho use as Figure 4. Sd is not. These seemingl y s imple acts of object identification require a lot from the wJrnt pathway, and they cons titute the main topic of the res t of this chapter.
Like m any seemin gly s imple acts, object percepti on is actuall y a collecti on of complex and remarkable accompli shments. Sensation and Perception covers in detail the perceptual processes related to vision and hearing, taste and smell, touch and pain as well as the vestibular and proprioceptive systems. Individual chapters cover separate topics including the fast-developing areas of perception of emotions and attractiveness and recognition of faces, plus newer topics.
Home Introduction To Sensation Perception. Sensation and Perception. Sensation and Perception by Jeremy M. Wolfe,Keith R. Kluender,Dennis M. Levi,Linda M. Bartoshuk,Rachel S. Herz,Roberta L. Klatzky,Daniel M. Sensation and Perception by Bennett L. Schwartz,John H. Related titles. Carousel Previous Carousel Next. Gray Crawford - Assimilating Hyperphysical Affordances. Jump to Page.
Search inside document. Wertheimer, Those psychologists discovered a number of important principles that are valid for visual as well as auditory stimuli.
Bottom-up processing: Organizing perceptions by beginning with low-level features. Himanshu Masand. Sreeharsh Unnithan. Fahimul Fahim. Mauricio Piatti. Zosima Masangcay. Eyahyn Pang's Jabonillo. Viji Youandme. Debora Silveira. Aaron Agyemang. Tomas Barbaglia.
Sensation and Perception, Sixth Edition is newly available in a more affordable paperback version, making it ideal for undergraduate students. The sixth edition retains the clear organization of previous versions, covering a wide range of core topics, from skin senses such as touch to chemical senses such as taste and smell, to our complex visual and auditory sensory systems.
This book is essential reading for undergraduates and postgraduates studying courses on sensation and perception. Why does ventriloquism work, and why can airliner flights make you feel disoriented? The answers to these and other questions about the human senses can be found within the pages of Foundations of Sensation and Perception.
This third edition maintains the standard for clarity and accessibility combined with rigor which was set in previous editions, making it suitable for a wide range of students. As in the previous editions, the early chapters allow students to grasp fundamental principles in relation to the relatively simple sensory systems smell, taste, touch and balance before moving on to more complex material in hearing and vision. The text has been extensively updated, and this new edition includes: a new chapter devoted to attention and perception over new references over 30 new figures and improved, more colorful, visual presentation a new companion website with a range of resources for students and lecturers The book contains a range of pedagogical features, including tutorial sections at the end of each chapter.
This distinctive feature introduces areas of the subject which are rarely included in student texts, but are crucial for establishing a firm foundation of knowledge. Some tutorials are devoted to more advanced and technical topics optics, light measurement, Bayesian inference , but treated in an accessible manner, while others cover topics a little outside of the mainstream music perception, consciousness, visual art. Foundations of Sensation and Perception will enable the reader to achieve a firm grasp of current knowledge concerning the processes that underlie our perception of the world and will be an invaluable resource for those studying psychology, neuroscience, and related disciplines.
Sensation and Perception Author : E.
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