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I am confused about this question. Can someone explain this?
Here are my thoughts:
I know Weber's equation is delta I = kI
Looking at the change from 2 to 2/3 to 2/9, it seems that the stimulus intensity is decreasing by a factor of 1/3
This would suggest that the intensity of sensation should also be decreasing, so I was able to eliminate choice B and C
Choice D seems close to the decrease by factor of 1/3
Can someone explain stimulus intensity and perceived intensity in terms of Weber's Law?
This is a confusing-worded question which I think gets some of the basics of Weber's Law confused (for example the actual change in weight or units need NOT be the same magnitude to create a just noticeable difference. It is a fixed ratio.
I actually don't know psych well (yet!) so this is just based off the reasoning provided in the "Why" section:
It says as the stimulus intensity changes geometrically (multiplied by a fixed non-zero number), the perceived intensity of the stimulus varies arithmetically (difference in consecutive terms is due to a fixed amount). In this problem the stimulus intensity decreases each time by 1/3. The
only answer choice where the perceived intensity of the stimulus varies by a fixed amount is choice A (-.25 each time).
arithmetic sequence:
https://en.wikipedia.org/wiki/Arithmetic_progression
geometric sequence:
https://en.wikipedia.org/wiki/Geometric_progression
It is the intensity of SENSATION the question is asking about. Not the stimulus. Otherwise for the same person (which as far as we know it is) the change in stimulus would have to adhere to the same 1/3 ratio.
Weber's law states the proportion of stimulus change needed to obtain a change in perception is a constant:
ΔI/I = K
For example if I place a 1 kg weight in your hand, and add smaller weights until I get to 1.25 kg before you notice a difference, your just detectible threshold = 0.25/1 = 25%. Meaning no matter what weight I start with, you should not be able to detect any difference until the weight changes by at least 25%. if I gave you 100 kg, Weber's law states that you would not detect a difference until you reach 125 kg.
In this example, what (I think) they meant to say was:
Going from 2 to 2/3 units of stimulus resulted in a noticeable difference. The factor of change here was 1/3 or -66%
Going from 2/3 to 2/9 units of stimulus resulted in a just noticeable difference. The factor of change here was 1/3 or -66%
The way I read this question, they ask about the intensity of the SENSATION after providing info about the intensity of STIMULUS. The equation you reference refers to calculating the intensity of the stimulus. You are correct in that reducing the STIMULUS by a factor of 1/3 each time would expect a just noticeable difference for this person, but NONE of the answers provide such a ratio. That is because they are asking about the change in intensity of the sensation, not the change in stimulus (aka weight, brightness, loudness....).
The only SENSATION change provided which follows a constant pattern (like the provided stimulus does) is choice A.
This question is definitely an odd duck, and can be challenging. To me it seems more like an psych question rather than an MCAT psych question.
hope this helps, good luck!
