What is the connection between physics and psychology?

Traditional Psychophysical Methods

I. Measurement of Sensory Threshold

Sensory threshold (sensory threshold), also known as threshold limit, is the core concept of traditional psychophysics. Threshold can be divided into two kinds: one is absolute threshold (absolute threshold), usually abbreviated as RL (German Reiz Limen), which refers to the size of the stimulus that can just cause psychological feelings; the other is differential threshold (differencethreshold), usually abbreviated as DL (German Differenz Limen), which refers to the amount of stimulus change that can just cause differential feelings. DL (German Differenz Limen), which refers to the amount of stimulus change that is just enough to elicit a differential sensation. However, although the threshold is theoretically the "all-or-nothing" mutation point of psychological feelings, in fact, such a definition of the threshold is not useful in the actual measurement of the threshold. Practical research tells us that for a given intensity of stimulation, subjects sometimes report "no sensation", sometimes "sensation", and sometimes "a little sensation". Therefore, when confronted with the concept of threshold, the experimenter must resort to an operationaldefinition. Since the distribution of the individual's sensibility at all moments basically conforms to the normal distribution, according to the principle of statistics, the smallest stimulus intensity that can just cause sensation can be expressed by its arithmetic mean, and this mean is exactly the stimulus intensity that is reported to be "sensed" in 50% of the experimental times, so the threshold can be set as the operational definition. Thus, the threshold can be operationally defined as the value of the stimulus that elicits a response in 50% of the experiments; similarly, the difference threshold is defined as the difference between the intensities of the two stimuli that elicit a difference in sensation in 50% of the experiments.

It was on the basis of these operational definitions that Fechner devised three methods of measuring sensory thresholds -- the minimum variation