LEC 3 pimb - The Weber Fraction PDF

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The Weber Fraction...

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LEC 3: PIMB We are trying to identify our sensitivity towards certain stimuli.

Weber came up with weber law, which as the weber fraction: it is the measurement of how sensitive we are in differentiating (difference threshold) two stimulus.

The Weber Fraction: revisited (see lec article) STUDY

They explored the approximate number system (i.e. our ability to determine quantity) and the difference between children and adult in providing this information. Weber fraction was used to see if human beings are born with the ability to differentiate between quantities or does it grow over time. To test this, researchers collected participants from different age groups (3-,4-,5-, and -6 year olds and adults). On each trial, participants were asked which of the two options presented to them had more quantities. Results showed that the weber fraction was lower in adults than children, indicating that younger participants have more difficulty in finding out the difference threshold. Thus, with the help of weber’s faction, it was possible to find out that the approximate number system develops as human beings age over time.

. what is the difference between children and adult. -used weber fraction to see if we were born or we developed over time. They are looking at the acuity (sensitive) we are with differenting different quantities. they texted diff age groups Methodology: They asked give age groups (16 p) 3-,4-,5-,6-, year olds and adults 4 practice trials followed by 66 test trials participants asked to pickbox with the greater quantity (two boxes) and verbal feedback given throughout. different ratios in box : eg 1-2,3-4 etc. both bpxes are shown different ratios of objects inside box. results: adults have lowest weber fraction (i.e. more sensitive we are in differentiating change, and so the

differential threshold is small. We will need least amount of change between stimuli to see the difference. in other groups, the weber fraction gets larger. This tells us that when we are young it is not that simple to determine differences between quantities/. ---Back to thresholds, what can we do with them? Collection Psychometric data -more complete account of stimulus? characteristics (google more) -we get psychometric function Thresholds doesn’t give us a complete picture. It only tells us sensitivity under that specific condition. To get a complete picture, we have to test on varities of stimulus conditions. -measure AT or DT multiple times we need to vary the stimulus dimension of interest eg. Tone frequency. This collection of psychomentric data (thresholds) is referred to as a psychophysical function. e.g sound: usually we motigfy the change of the intenstity of sound. When intensity drops so does our ability to notiece it. we get psychophysical functions: eg. Hearing: which age has better hearing? psychophysics helps us VISION AND AUDIO when the y are the most sensitive etc -visual acuity and the CSF visual capability of diff animals --

ing what infant sees are lower perceptual abilities than adults. This is good because know we can guide their education. Toys (have high contrast colors in order to be able to see them properly), play, etc. psychophysics allows us to measure this ability. i.e. what they see

soo…. Psychophysics. We know what it is. we are seeing the impact of psychophysics. example: psychophysics has developed models and methods of loci compressions, i.e. MP3. we would have never known MP3. The way they work they take into account our perceptual abilities. It

removes all the things we don’t require coz we cant perceive it. That’s why its called lossi compression (we lose what we don’t neeD). Mp3 knows the frequency etc we can hear? Google. Auditory masking because of our knowledge of psychophysics and different thresholds and how they can shift and mask certain frequencies that we cant perceive.

The Mosquito device people started having outside young people hang out. This device emits high frequency sound that’s annoying and causes people to immers. This tone is however only heard by young people. Heard by those under 20. Contriversial. The teen Buzz Tone old people can hear and not younger.

Perception of body size -method of constant stimuli to dderive measures of self-percieved body size. -methods were made years ago and are still getting used of psychophysics (can put intro or anywhere) How accurate they are with their body estimates (body image distortion) and sensitivity in discriminating body size (body image sensitivity) and then correlate these results to other standardized measures like disordered eating. quickly to go back: method of constant stimuli. Task is to measure which shade is stronger or weaker. Then you can derive a data on graph that shows which ones are stronger than what. So we then get the psychometric function. Then from the 50% mark at the graph, known as the point of subjective equality. This is the point where they cannot see a difference between the shades. i.e. they’ll just chose stronger or weaker coz cant decide between the two. We can also establish two more points i.e. 75% and 25% when we average these quantities, we find the Differential threshold.

Anyway back the body one. So full body imaggeds of each participant was taken. These images were distorted. i.e. made wider or thinner. -5 were wider than orginal (Either 4%,5%, etc) -5 that were narrower (4%...20%) -they did not use the actual photo. they have to respond saying is it wider or narrower than their body. 100 trials. Each photo presented 10 times. then with this you can dervive these psychometric functions. Calculate PSE: the body distortion that corresponds to self-perceived body size. i.e. middle of graph. Calculatr IU: internaval of uncertainity. The 75% and 25%, devided by 2. Tells us the body image sensitivity. ----Two examples of neuroimaging studies that have measured some aspects of brain functions and have related it to psychophysical function too. This is done so that they can determine something about what guides ojur perception. Study 1: Perception of symmetry. study name: symmetry activates extrastriate visual cortex in human and non hjuman primates.

What they did: brain activity when they see pattern of symmetry: it activateds specific areas of brain. However if shown random dot pattern, then broad region in the brain is activated. so know we know which places are active when we see symmetry, but does that mean that it is these regions that facilitate our processing of symmetry. ? how to we perceive symmetry? to find out: psychophysics. by calculating the correlation between psychophysicl and fmri measuremtns, it is possible to quantify which cortical visual areas are most likely to mediate the perception of symmetry. The brain is folded instead of brain being massive. Anyway, in addition to folding the brain, we can make it a flat sheet to see the the areas that are active. The visual areas are shown to be active. What we know is that it is prefferiatially activating certain areas of the visual system and not all. Thus, the places that are active are associated with processing of symmetry. But is it also the reason for the perception of symmetry?

So with the help of psychophysics. Psychophysic task: by calculating the correlation between psychophysicl and fmri measuremtns, it is possible to quantify which cortical visual areas are most likely to mediate the perception of symmetry.

Asked if symmetrical or not. Imagine out of 100 dots we remove some. That means you’ve made it not as symmetrical as it was before. If we carried on and kept moving on, we have reduced ability but we can still establish some kind of symmetry. the response to different level of symmetry of a particular area, we see if there is a similar pattern than of the symmetry. Correlation betwee the psychophysics response to the stimuli is closely associated with the neural response of stimuli. This tells us that our perception of symmetry is because of whats going on in this area of brain.

Study 2: Dyslexia -parts of the brian that might be associated with dyslexia, and also the theory called magnocellular theory of dyslexia. It says that d might arrive because of a deficit in the magnocellular pathway. This pathway is important as it is one of the two pathways that send visual info to the brain. study measured the perceptual thresholds for speed discrimination. And also measured reading perfomarnace. They measured their brain activity in two regions, knwn as the primary visual cortex and middle temproral area (Associated with motion). They have low luminance (brightness). Contrast was also modified. Brain response goes down when the contrast goes down. Brain response in dyslexic patients in MT goes lower than normal patients. For V1 it was same between control and d group. conclusion: -the data indicates a strong 3 way correlation between brain activity, speed discrimination thresholds, and reading speed. -higher V1 and MT responses= lower perceptual thresholds=faster reading -the M pathway deficit could only be a correlate of dyslexia there are more readings that you can do: see link at the end of lec. Essay - a couple of paras of Fechner and weber fraction Fechner tells us how stimuli needs to differ in order for us to perceive differences around them. he has a small equation to describe it. That’s all. weber fraction is a measure of sensitivity. Smaller the fraction the more sensitive we are to differeiate

between two stimuli. This is because the fraction tells us how much stmuli needs to change by so we can perceive differences. Fraction is small then differences is small. So we are highly sensitive to find the differitate. -he would apperiate if you go on talking about webers law and differencs between stimuli, how stimuli needs to be different for us to perceive it, then it would be great.

Use clarivate analysis website. Walk.me mas .ac.uk web of science

-should we talk about fechners methods? Constant stimuli etc. NO. you don’t have to talk about the three methods. -you want to talk about the thresholds, AT,DT etc. that Fechner was describing in his logirtoium law. Depends on how you structure it. Steven’s for the development section of essay. He challenged Fechner assumption that relationshop between stimuli and etc. fechner’s method improvement : staircase techniwues, forced choice techniques, etc. don’t have to mention. you want to mention studies that relate to weber and Fechner and use it, eg. In animals infants etc. S and law is the same thing....