Weber's law and thresholds (video) | Khan Academy
These parameters include the type of electric stimulus (for example, The function of the strength-duration relationship can be fitted with a. The strength–duration relationship for extracellular stimulation is often assumed a biophysical basis for understanding stimulation dynamics and guidance for. Recently, the relation of fibre diameter to the rising and relationship between stimulus intensity and rate of rise of the msec. duration were delivered at and per second from an .. Hudakova for her advice on the statistics, and to the.
Thus if the stimulus is too small, the membrane potential never reaches threshold. When examining the Strength-Duration relationship in a nerve trunk, containing thousands of nerve fibres, one must be careful to consider which of these many fibres the threshold in question pertains to. The threshold stimulus voltage for the CAP as a whole is actually the threshold for the fastest, most excitable fibres in the nerve.
As it is difficult to accurately determine this threshold, the procedure outlined below uses as a reference signal a CAP whose peak amplitude is about one fifth of Maximal. Thus this threshold is clearly the threshold for another less excitable group of fibres. Procedure To begin, the stimulus duration is set to 1. The stimulus voltage is increased slowly until a CAP appears. In this example, we have adjusted the voltage until the CAP amplitude fills two intervals of the horizontal grid on the screen.
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This CAP amplitude will be used as a reference for the rest of the experiment. Another reference line can also be chosen, provided it is kept throughout the exercise We read the stimulus voltage from the stimulator, and the corresponding stimulus duration in this first case 1 ms and enter this pair of values into a table. Thus this stimulus duration and voltage have brought to threshold a small group of excitable fibres in the nerve, although they are not the most excitable.
Most people would probably notice this new increase, this new weight. Basically, what I'm trying to say is that a addition of. The threshold at which you're able to notice an increase or a change in weight or really any sensation so that threshold, where you go from not noticing a tiny little change to actually noticing a tiny little change is known as the just noticeable difference, noticeable difference.
We can abbreviate this as JNT. In this case, the just noticeable difference, let's say for just sake of argument, is. Let's imagine that instead of starting with a two-pound weight, instead, we started with a five-pound weight, so five-pound weight.
The five-pound weight is much heavier than the two-pound weight. In this case, if I replace the five-pound weight with a 5. Basically, what's going on here is that since you're using more muscle fibers, you're using more sensory neurons, they're not as sensitive to small increases.
They're not as sensitive to the 0. You need a bigger just noticeable difference in order to actually be mentally aware of the change in weight. Basically, when you're holding five pounds, let's say for sake of argument, the just noticeable difference is a little bit higher than when you're holding two pounds.
Now, these numbers we're just throwing around, and if you actually did this experimentally, the actual numbers might be different, but the concept generally would remain the same. In the five-pound weight category, the just noticeable difference is.
From this, we can come up with an equation.
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Let's just define some variables. I, or the intensity of the stimulus, is equal to two pounds in this case and five pounds in this case. And delta I, so delta I, would be the just noticeable difference. It would be 5. For the five-pound example, I would be five, and delta I would be. Basically, there is actually a guy back in the day named Weber. Weber noticed in that the ratio of the increment threshold, the ratio of the increment threshold, which is this over here, to the background intensity, which is this over here, so this is the background intensity, is constant.
If we were to take. That's what Weber's law is.
Weber, inrealized that there is this relationship. We can write this as an equation. Delta I over I equals K. K is a constant for each individual person. There is this particular threshold, and the ratio, the background intensity to the incremental threshold is relatively constant, and that constant is this K value.
This part of the equation over here is known as the Weber fraction. This works for sensory tactile stimuli like lifting a weight but it also works for auditory stimuli. Imagine you're in a quiet room.