Lecture
In a psychophysical experiment, stimulus factors serve as the independent variable (IV). The physical parameters of the stimuli are varied experimentally, and the corresponding subjective characteristics are established empirically in accordance with them. The subjective series of sensations is measured by constructing scales of the participants' responses (both verbal and nonverbal).
The measurement goal pursued here (the construction of a subjective scale) brings to the foreground the problems of establishing quantitative laws that represent functional relationships between measurements of the stimulus series and the dependent variable (DV) of the subjective series. However, the problem of causal interpretation is pushed into the background.
It is necessary to distinguish between scales that reflect qualitative and quantitative changes in psychological variables.
Testing hypotheses about quantitative regularities usually involves conducting a multilevel experiment, in which the IV is represented at least on an ordinal scale.
A quantitative representation of an experimental relationship is also possible when the levels of the experimental factor (IV) are given on a nominal scale.
For example, diagrams and histograms reflecting quantitative indicators of the DV (on the X-axis of these histograms there is a nominal scale – the levels of the IV).
Moreover, a quantitative relationship can be established even when the DV is qualitative in nature.
For example, Fechner's law: the IV – the strength of the stimulus – is measured quantitatively, while the DV is represented by «yes» and «no» responses.
- Ebbinghaus's experiment on the memorization of meaningless syllables.
The DV was the frequency of correct recall of the words in the sequences presented to the participants (n – the position of the word in the sequence). A regularity was found: the edge effect – independently of the level of the IV (the syllables were equated for difficulty), the first and last syllables of the series were remembered better.
- The Yerkes-Dodson law – the optimum of motivation. Three degrees of task difficulty (three curves). The discrimination by mice between lighter and darker tunnels. Motivation was regarded as a magnitude linked to the strength of the electric shock, which served the function of reinforcement in learning. The mouse learned to avoid the shock by choosing the correct tunnel. For each degree of difficulty there was its own optimal degree of electric shock. Later the law was confirmed with humans. This is a demonstration of the simplest functional relationship pertaining to quantitative research.
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