Psychophysics and Fechner's Law – Sensory Processing (PSY, BIO)

00:01 Now let’s get into something called psychophysics or Fechner’s law.

00:06 So Fechner, our good friend Fechner, was actually a student of Weber who generated Weber’s law.

00:10 So this is sort of a furthering or a variant of Weber’s law.

00:15 And it’s imparting some of the information, but there’s a small twist to it.

00:19 So psychophysics quantitatively investigates the relationship between physical stimuli and the sensations and perceptions that they affect.

00:27 So what it’s doing it’s actually bringing some of the -- it’s bringing some of the onus onto the subject.

00:33 So the person who’s perceiving the stimulus.

00:35 So Fechner describes a logarithmic relationship between perceived intensity of a stimulus versus the actual physical stimulus intensity.

00:42 So a lot of words, let’s break that down into simple English.

00:44 So what we’re saying is as a subject, what you’re perceiving in terms of change is a little bit different than the actual change that’s happening.

00:55 So, when I say to you, “Can you detect a change in brightness?” For you arbitrary units, you can say if this level of brightness is unit one, how much until I see a change? I’m going to call that unit two.

01:09 Now that difference that we’re seeing might not be exact compared to the difference that we’re physically seeing, actually seeing.

01:16 So we’ve described actually a logarithmic relationship and that logarithm relationship is the Fechner’s law.

01:23 And so we’ll kind of walkthrough an example of that that helps us.

01:26 And that’s -- it’s looking at, say, stars.

01:28 When you’re looking at a star through a telescope and you detect a certain level of brightness, you might look at other stars around.

01:35 And I say to you, look and find me another star that’s just a bit brighter, like that’s the next closes level of brightness.

01:45 And you’re going to look in your telescope and you’re going to say, “Oh, the one here to the right.” That one is just a smidgen brighter.

01:54 Now that smidgen is a personal unit that you’ve arbitrarily assigned and that’s your perception of brightness.

02:00 But that is actually, if you’re looking at lumens of brightness, the number that we’re going to get is going to be a logarithmic scale of what we’re actually perceiving.

02:09 Okay. So that relationship is really what you need to understand.

02:12 So in terms of the MCAT, you’re not going to be put through a Fechner’s law actual mathematical question.

02:18 Most likely, they're going to want you to know that that relationship exists and that it’s a logarithmic relationship.