Term
| What does Gregory argue about the role of knowledge in perception? |
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Definition
| Gregory argues that we construct internal models of the world over time, and that we need past knowledge to infer what we perceive. |
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Term
| What does Gregory argue is/are the sources of knowledge of the world? In your answer, give the term(s) Gregory uses for the source(s). |
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Definition
| Gregory argues that there are two kinds of learning; phylogenetic (a fancy term for innate) and ontogenetic (memory). |
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Term
| What does Gregory argue about the idea that sensations provide clues to the outside world? In your answer, include Gregory’s concept of hypotheses. |
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Definition
| Gregory argues that perceiving in similar to hypothesizing. Sensations provide clues similar to rationales that justify our predictions about what is occurring in our environment. |
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Term
| What does Gibson argue about the role of knowledge in perception? |
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Definition
| Gibson argues that the role of knowledge is only to be aware of one’s surroundings, and information is neither transmitted nor stored. |
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Term
| What does Gibson argue about the idea that sensations provide clues to the outside world? |
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Definition
| Gibson argues that sensations are not clues but rather the importance lies within the object itself. He also argues that information is actively gathered from the environment and that it is not stored. |
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Term
| What does Gibson argue is/are the source(s) of knowledge of the world? |
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Definition
| Gibson argues that knowledge does not come from a distinct source, but it is attained by actively exploring our environment. |
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Term
| Are there important differences in Gregory and Gibson’s argument about how knowledge of the world is acquired? |
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Definition
| Yes. Gregory argues that we have previous knowledge and that we build internal models to perceive, while Gibson supports the idea that we are continuously actively sensing our environment by gathering the information that is readily available to us. These arguments give us two different views of how we perceive through experience. |
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Term
| List 4 categorically different types of applications of psychophysics: |
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Definition
| Threshold measurement, stimulus detection, magnitude estimation, multidimensional scaling |
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Term
| What is the simplest idea of an absolute threshold? |
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Definition
| The minimum stimulus intensity that a person can detect |
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Term
| What sort of functional relationship should it produce between stimulus intensity and perception of the stimulus? |
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Definition
| The ideal relationship between stimulus intensity and perception of stimulus should be an abrupt transition from not detected ever to being detected every time. |
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Term
| How does that simplest idea of the relationship between stimulus intensity and perception of the stimulus differ from the experimental results of real psychophysical studies? |
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Definition
| The actual relationship between stimulus intensity and perception of the stimulus is instead represented by an s curve that increases gradually from never seen to always seen. |
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Term
| How do psychophysicists deal with the variability of absolute threshold when trying to identify absolute thresholds in their data? |
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Definition
| Psychophysicists set the absolute threshold at the stimulus intensity where the stimulus is detected 50 percent of the time. |
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Term
| List Fechner’s 3 psychophysical methods: |
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Definition
| Method of Constant Stimuli, Method of Limits, Method of Adjustment |
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Term
| Describe the commonalities of all 3 of Fechner’s methods. |
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Definition
| All methods use yes/no or stronger/weaker answering. The stimulus is present or it is not, the stimulus is stronger or weaker. All methods present only one stimulus at a time or only two stimuli for difference threshold. |
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Term
| List 2 fundamental problems with Fechner’s psychophysical methods, giving an example of each: |
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Definition
| Two problems with Fechner’s psychophysical methods are the problem of intrinsic light and you can’t separate true perceptual sensitivity from decision factors. When you are in a dark room or even a dark cave you will still have random firing in the brain which causes you to see light that isn’t exactly there. You can’t separate bias from sensitivity. In the case of a doctor the bias may be more conservative if a hit requires more investigation by a painful procedure, whereas it may be more liberal if what could possibly be there is life threatening. |
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Term
| What is the most fundamental improvement Signal Detection Theory makes over Fechner’s methods? |
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Definition
| It is able to separate bias from sensitivity. |
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Term
| What is the key methodological difference between the methods of Signal Detection Theory and Fechner’s methods that allows for the above improvement? |
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Definition
| The methodological difference between the method of Signal Detection Theory and Fechner’s methods is the use of “catch trials” trails where stimulus is not present and calculating the percentage of false alarms (saying there is a stimulus when there is not) and comparing it to the percentage of hits (correctly identifying a present stimulus). |
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Term
| Give the Equation for Weber’s Law and its algebraic corollary. |
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Definition
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Term
| Describe Weber’s Law using normal language. |
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Definition
| Change in stimulus intensity (ΔI) equals some constant (K) multiplied by the original stimulus intensity. We can find the constant (K) by dividing the change in the stimulus by the original stimulus intensity. |
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Term
| Give a simple but original example of the operation of Weber’s Law: |
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Definition
| When my boyfriend and I are driving in the car he likes to listen to the music loudly, but I can’t stand loud music. When I tell him to turn it down, he barely turns the radio down. To me it still sounds the same intensity. Therefore the change in the intensity of stimulus was less than K; therefore the change in intensity was not detected. |
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Term
| What was Fechner’s goal in creating his theory, known as Fechner’s Law and what role did Weber’s Law play in it? |
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Definition
| Fechner used Weber’s law as a model. He discovered that sensation intensity did no increase linearly with increasing stimulus intensity. He transformed the equation using log such that the magnitude of subjective sensation increased proportionally to the logarithm of the stimulus intensity. S = k*log (I), Sensation Intensity = K*log (Stimulus intensity). |
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Term
| Describe the fatal flaw that Stevens pointed out with Fechner’s Law, and give an example to illustrate it. |
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Definition
| Stevens demonstrated that the JND is not a ratio scale. JND size increases with perceived intensity such that a light that is in essence twice as bright as another light is seen as more than twice as bright. A ratio scale of measurement means that you can make comparisons between stimuli such that 4 feet is four times as long as 1 foot. |
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Term
| Describe Stevens’ psychophysical method of direct scaling used to investigate the relationship between stimulus intensity and perceived intensity. |
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Definition
| Direct scaling is a set of psychophysical procedures for measuring subjective sensory experiences such as loudness or brightness. These procedures are based on the assumption that people can rate sensory magnitude. People are presented with stimuli of different intensities and asked to assign a number to each stimuli using whatever scale they wish. Then their scores are standardized and compared to the “true scale”. People are surprisingly accurate. |
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Term
| Give the equation for Steven’s Law: |
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Definition
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Term
| Describe Steven’s law using normal language. |
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Definition
| Sensation intensity = physical stimulus intensity raised to some power. The magnitude of subjective sensation is proportional to the stimulus magnitude raised to some exponent. |
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Term
| The functional relationships between stimulus intensity and perceived intensity differs according to Stevens’ Law depending on whether the exponent is <1, 1, or >1. Explain each of these 3 relationships; give its name and an example for it. |
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Definition
<1 compression, physical increases are underestimated. Brightness
>1 expansion, physical increases are overestimated. Salt
1 accurate, physical increases are perceived accurately. Line length. |
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Term
| Using the information given below produce the appropriate 2x2 SDT contingency table with the H, F, Miss, and CR rates. In addition, using the formulae for d’ and c describe how sensitive the subject is, and what degree and sort of bias he/she has. (a) 100 trials each of signal present and absent. (b) 89 “Yes” responses for signal present trials, and 76 “Yes” responses for signal absent trials. |
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Definition
| | | | Response | | | | Yes | No | | Stimulus | Present | 89 | 11 | | Absent | 76 | 24 | d’ = z(H) – z(F) c = -.5 ( z(H)+ z(F)) d’ = z(.89) –z(.76) c=-.5 ( z(.89) + z(.76) ) Has an extreme liberal bias, and little sensitivity. |
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Term
| For this question you will come up with your own numbers that fit the criteria listed below. Using the information given below, produce an appropriate 2 x 2 SDT contingency table. (a) 100 trials each of signal present and absent. (b) The subject is very sensitive and has a very conservative bias. |
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Definition
| | | Response | | | | Yes | No | | Stimulus | Present | 72 | 28 | | Absent | 11 | 89 | |
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Term
| Draw the decision space proposed for SDT, given the following different scenarios: 1) no sensitivity, but a very conservative bias; 2) very high sensitivity, with a very liberal bias. |
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Definition
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Term
| Draw the ROC curves, with each axis labeled, for the above two scenarios. |
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Definition
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Term
| What are the units in which d’ is measured. |
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Definition
| Since we transform the hit rate and false alarm rate into standard scores, the units of d’ are in z or standard units. |
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Term
| What does it mean to say that d’ is assumed to have the distance properties of 1) positivity and 2) unboundedness? |
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Definition
| Positivity refers to the idea that all distances are positive. When you relate d’ prime to distance we can then say that the distance from a to b is longer than the distance between c and d. Unboundedness refers to that there is no maximum value of d’. |
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Term
| Suppose you do an experiment, and you find that a subject has a negative d’ value. What does this mean, and what could have caused it? |
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Definition
| When a participant has a negative d’ value it means that he has a larger proportion of misses and false alarms than hits and correct rejections. This may have been caused by a misunderstanding of directions. |
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Term
| Suppose you run an experiment and do a Signal Detection analysis of the data. Why is it a problem if data for a subject in a Signal Detection experiment includes H or F rates of 1 or 0, and what is the general solution? |
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Definition
| If an experiment produces H or F rates of 1 or 0, then it means that the participant has an extreme liberal or conservative bias. The general solution is to re-run the experiment telling the participant different instructions trying to sway the bias towards the middle or calculate the ROC curve and determine sensitivity without bias, calculate d’. |
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Term
| What does it mean to say that an ROC isosensitivity curve is regular? |
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Definition
| A participant that displays a particular pair of hit rate and false alarm rates on an ROC curve should theoretically be able to sway their bias to produce any hit rate and false alarm rate on that curve. |
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Term
| What do different points on an ROC isosensitivity curve represent? |
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Definition
| Different points represent different biases. As you go up on an ROC curve your bias is more liberal, a higher hit rate, but also a higher false alarm rate. |
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Term
| According to Macmillan and Creelman, which theoretical approach to perception does SDT belong to, direct or indirect, and why? |
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Definition
| The detection theory is part of the indirect approach because an intelligent, not entirely reliable process makes inferences about them and acts according to the demands of the experimental situation. The constructionist decision processes of detection theory mark it as an early example of cognitive psychology. |
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Term
| The Signal detection measures, d’ and C, are both calculated using H and F. What is the key (or fundamental) difference in their calculation? |
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Definition
| The difference is that for calculating d’ we take the difference between the z transforms of the two rates, whereas in the calculation of C we add the two measures and multiply by negative .5. |
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Term
| Explain why it is that the calculation of the criterion, c, involves summing H and F? |
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Definition
| When we are calculating c we are trying to find the bias, so we find the proportion of the bias in the hit rate and the proportion of bias in the false alarm rate and we add those two proportions together. Since we are adding proportions we divide by two to take the average “bias” between the two measures. |
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Term
| What is the value of the criterion, c, when decision making is unbiased? |
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Definition
| The value of c when the decision is unbiased is 0. Because negative values are a tendency to say yes and positive values are a tendency to say no. |
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Term
| Suppose the criterion, c = 1.75, and d’ =1. What is the value of the relative criterion, c’ and why? |
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Definition
| c’ = c/d’ c’= 1.75/1 = 1.75. The relative criterion is the same as the calculated criterion because it is dependent upon d’ which is relatively low. |
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Term
| If the value of the criterion, c = 0, what is the value of the likelihood ratio, ? In giving your answer, sketch the two distributions (X|S1 and X|S2), and the criterion c as they should appear in this situation. Also, write out the formula for the likelihood ratio, and indicate its relation to the sketch: |
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Definition
| =ecd’ =e0=1 "need sketch" |
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Term
| According to SDT, as signal strength increase, what should happen to d’, and why? What should happen to the criterion, c? |
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Definition
| As signal strength increases, d’ should also increase, because it should be more distinguishable between stimuli present and stimuli absent. C should approach 0, towards no bias. |
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Term
| If you look at the isobias curves for c, we find that, consistent with the assumptions of SDT, as F increases, what happens to H? Why must this be so? |
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Definition
| As F increases, H increases because if d’ is constant then as bias changes the proportion of hits and false alarms must change. Draw figure. |
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Term
| According to the SDT criteria that a bias measure should 1) depend monotonically on H and F in the same direction, and 2) be independent of sensitivity, which measure(s) of bias is(are) best? |
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Definition
| The measures of bias that are best are the ones that are independent of sensitivity. Since Beta and c’ both depend on d’ the best measure of bias is c. |
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Term
| Describe the difference in eye placement found between predators versus prey, giving examples of each. |
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Definition
| Cats, a predator animal, have different eye placement than rabbits’ eye placement. The predators’ eye placement is more towards the front of the face. Vision does not extend 360 degrees. There is more binocular vision, but there is a blind spot. The more binocular vision increases depth perception which is helpful in distinguishing prey from foliage. In the prey animals, eye place is toward the side of the face. The range of vision is 360 degrees, but has very little binocular vision. This is advantageous for prey animals because they can be aware of what is around them without having to turn their head to look all the way around, but they don’t have very good depth perception which isn’t always necessary. |
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Term
| What is the survival advantage for prey animals of their eye placement? |
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Definition
| Prey animals are able to look all the way around themselves without having to move. This doesn’t give any motion cues for the predator to pick up on. |
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Term
| What is the survival advantage for predators of their eye placement? |
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Definition
| Predator animals with their eye placement have greater depth perception and can detect prey that may be camouflaged. |
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Term
| What is the refractive error associated with myopia? |
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Definition
| Focus of light is in front of the retina. |
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Term
| What is the anatomical eye defect that produces myopia? |
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Definition
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Term
| What type of lens correct myopia? |
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Definition
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Term
| How does a concave lens correct the refractive error associated with myopia? |
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Definition
| The concave lens spreads the light, so that it takes more distance for the light to converge. This helps the long eye. |
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Term
| What is the refractive error associated with hyperopia? |
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Definition
| The focus of light his behind the retina. |
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Term
| What is the anatomical eye defect that produces hyperopia? |
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Definition
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Term
| What type of lens corrects hyperopia? |
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Definition
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Term
| How does that type of lens correct the refractive error associated with hyperopia? |
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Definition
| It helps converge the light faster. So that the light converges on the retina of the short eye. |
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Term
| What is the immediate cause of the blind spot? |
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Definition
| The optic nerve needs to exit the eye and there can be no photoreceptors where it leaves the eye. |
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Term
| How is the immediate cause of the blind spot in turn cause by the seemingly strange layout of cells in the retina? |
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Definition
| Since the messages from the ganglion cells have to exit the back of the eye, there can be no photoreceptors there. |
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Term
| How does a seemingly more logical layout of cells in the retina of some other species avoid producing a blind spot in their eyes? |
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Definition
| The photoreceptors are at the front of the eye. The organization of photoreceptors to ganglion cells is flipped. |
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Term
| What function is served by the seemingly strange layout of cells in the human eye? |
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Definition
| The nutrients that are necessary for the function of the photoreceptor cells are located in the choroid at the back of the eye. |
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Term
| Explain why filling in the blind spot can be considered as support for Constructivism, and the idea of perceptions as hypotheses, using as an example the “wheel” blind spot demonstration we did in class. |
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Definition
| Constructivists (indirect perception) hold that we take bits and pieces of sensory information and infer their meaning from our previous knowledge. Since there is information missing where the blind spot is located, we take our best guess as to what should be there. We don’t see white in the wheel, we see the spokes, even if they weren’t there in the first place because our eye is taking what is around the spot and filling in “the best” guess as to what is supposed to be there. |
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Term
| Describe the relationship between visual acuity and photoreceptor density as a function of retinal eccentricity. |
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Definition
| Retinal eccentricity is the distance from the fovea (center of vision). As visual acuity decreases, retinal eccentricity increases, density of cones decreases, and the density or rods increases. |
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Term
| Describe the difference in visual acuity and sensitivity between foveal and peripheral vision. |
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Definition
| In the fovea, there is high visual acuity, lots of cones, but very low sensitivity. In the periphery, there is high sensitivity, lots of rods, but very low visual acuity. |
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Term
| Define the term “convergence” in terms of the ratio of photoreceptors to ganglion cells. |
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Definition
| Convergence means more than one photoreceptor for every ganglion cell. |
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Term
| Describe the difference in convergence between foveal and peripheral vision, listing the types of photoreceptors and ganglion cells that do or do not have convergence. |
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Definition
| In the fovea, where there are primarily cones, there is virtually no convergence because there is usually only one ganglion cell for every cone. As you move into the periphery, the amount of rods and convergence increase because there can be many rods to one ganglion cell. |
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Term
| What stimulus would produce the absolutely maximum possible response from an on-center/off-surround ganglion cell receptive field? |
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Definition
| Where the entire center is stimulated and none of the surround is. |
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Term
| What is the relationship between retinal eccentricity and ganglion cell receptive field size? |
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Definition
| As eccentricity increases, the ganglion cell receptive field size increases. |
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Term
| What is the relationship between visual acuity and ganglion cell receptive field size as a function of retinal eccentricity? |
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Definition
| As eccentricity increases, receptive field size also increases, but acuity decreases. |
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Term
| What is the relationship between visual sensitivity and ganglion cell receptive field size as a function of retinal eccentricity? |
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Definition
| As eccentricity increases, sensitivity increases and receptive field size increases. |
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Term
| Explain the above-described relationship between visual sensitivity and ganglion cell receptive field size as a function of retinal eccentricity using the idea of convergence. |
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Definition
| As convergence increases, sensitivity increases. There is greater convergence and sensitivity as retinal eccentricity increases. The convergence of cells increases sensitivity. |
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Term
| Why do you perceive illusory dots only at intersections of a Hermann Grid, but nowhere else on the grid? |
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Definition
| Because at the intersections there is more inhibition of white than other parts of the grid. Due to the extra inhibition of white, we see black or vise versa. |
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Term
| Why are you less likely to perceive an illusory dot on a Hermann Grid in your foveal vision? |
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Definition
| Because receptive field sizes are smaller in the fovea and therefore more likely to fit within the borders of the stimulus. |
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Term
| With what type of Hermann Grid are you most likely to perceive an illusory dot in the foveal vision? |
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Definition
| A small squared Hermann Grid because the illusion is stronger because the receptive fields do not fit inside the bounds. |
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Term
| According to Barlow, what changes in terms of the number of cells that are devoted to vision as one moves in the visual system from lower levels to higher levels? |
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Definition
| The number of cells devoted to vision decreases as you move from lower levels to higher levels. |
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Term
| According to Barlow, what changes in terms of the proportion of cells that are active at any one time that are devoted to vision as one moves in the visual system from lower levels to higher levels? |
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Definition
| Proportion of cells that are active at any one time decreases as you move from lower to higher levels. |
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Term
| What is Barlow’s psychophysical linking hypothesis? |
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Definition
| Whenever two stimuli can be distinguished, in normal life or in a psychophysical experiment, then proper analysis of the impulses occurring in a single neuron would enable them to be distinguished with equal or greater reliability. |
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Term
| Give a reasoned argument for why Barlow’s theory is consistent with either Gibson’s direction perception theory, or Gregory’s indirect perception theory, giving examples to support your argument. |
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Definition
| Barlow’s theory is consistent with Gibson’s direct perception theory. Barlow believes that a single neuron is sufficient to extract meaning. Therefore the simplest element of perception is a neuron. He doesn’t seem to agree that perception is constructed form many neurons in higher levels of perception. Also, he refers to Bartlett’s phrase effort after meaning which implies direct perception. Barlow holds that it is the objects themselves that have meaning to us; this information just has to be gathered. The gathering of information is consistent with the theory of Gibson’s direct perception. |
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