Individual differences in the classification of stimuli by dimensions.

Multidimensional scaling experiments were performed with "size" and "brightness" as parameters. Subjects (ss) had to rate the dissimilarity of pairs of discs differing in size or in brightness only, or in both parameters. It was then attempted to find a rule, by which the dissimilarity judgements of two-dimensional differences can be predicted from judgements given for the one-dimensional components. Minkowski-metrics were chosen as models, since for most of the ss the prerequisites for applying these metrics seem to be fulfilled. A simple procedure is described by which the one metric out of all Minkowski-metrics can be found which gives the best description for the data of a subject (Fig. 4). Although the task and the parameters used were the same for all ss, individually best metrics differed considerably, indicating individually different modes of perceptual analysis: Most ss adhered, roughly, to either the City-block or the Euclidean metric (cf. Fig. 10). (Only City-block metric was to be expected, since "size" and "brightness" are generally thought to be "separable" parameters.) In addition, there were three ss with metrics clearly different from both the City-block and the Euclidean metric (best exponents around 1.4). In view of those substantial differences between individuals one has to be cautious against the practice of averaging data from different ss.

Human pattern recognition: Individually different strategies in analyzing complex stimuli

Ronacher¹,

Bautz²

1985

Human pattern recognition: Evidence for a switching between strategies in analyzing complex stimuli

Ronacher¹

1984

In a preceding multidimensional scaling experiment, with "size" and "brightness" as parameters, subjects were found to use individually different strategies in processing compound stimuli: Most subjects adhered to either the Euclidean or the City-block metric (Ronacher and Bautz, 1985). In the experiment reported here, participants of the previous study were induced - by a manipulative instruction - to modify their strategy. With 5 out of 10 subjects a switching to another strategy occurred, which manifested itself in a drastic shift of the respective best metric (e.g. from Euclidean to City-block or vice versa). The extent and speed of changes as well as - in some instances - the stability of estimation accuracy show that subjects were not forced by the instruction to develop a new strategy. Results rather suggest that adult subjects have easily available two, or perhaps even more, alternative processing modes, the decision for one of them being a matter of a subject's preferences rather than of individually different abilities.

Perception of size and lightness of human observers: two criteria for holistic and analytic processing show no correlation in individuals

Ronacher

Süβ

1990

Results of a triad-classification task and a multidimensional-scaling (MDS) experiment are compared for individual observers. Both paradigms are designed to reveal whether stimuli are perceived in a holistic or analytic manner (Garner 1974). Subjects differed substantially and consistently in their triad classification pattern. The majority of subjects selected stimuli according to dimensional criteria; this classification type is thought to indicate an analytic stimulus processing. Approximately one third of subjects, however, used a classification according to overall similarity (indicating holistic processing). Except for the very first session, virtually no intermediate classification occurred. This clear separation into two classification types suggests that there actually exist two strongly preferred processing modes. Intraindividual variability between sessions in general was small. In one case, however, a spontaneous switching from a purely dimensional classification to a purely similarity classification occurred. This indicates that the observers have different processing options at their disposal, and are not forced to use a particular processing mode by the stimulus type--as has been supposed in the original concept of integrality/separability of stimuli (Garner 1974). In the MDS experiment also substantial interindividual differences in the "best-fitting" Minkowski metric were found, indicating different processing types. However, for individuals participating in both experiments, there was no correlation between the results of the two experimental paradigms. This is interpreted as a result of the subject's ability to choose between a few perceptual-processing options.