Changes in the Visual Threshold as a Function of Subception

Tachistoscopic and questionnaire methods for the measurement of psychological defences

Only few attempts have been made to compare different methods aiming at quantifying defensive strategies. In this study the tachistoscopic Defence Mechanism Test (Kragh, 1960b and 1985) is compared to paper-and-pencil tests of defence. There were virtually no correlations between the DMT and the other measures of defence. This may indicate that the concept of defence is a highly complex one. It is suggested that the Defence Mechanism Test may be measuring primary defence while defence questionnaires may be assessing more secondary forms of defence. The two questionnaires used for assessing defence correlated significantly, while a scale for social desirability showed no correlation with DMT or the two defence questionnaires.

Cross-modal induction of changes in sensory thresholds

Two experiments are reported in which subliminal stimulation of one modality with emotional material impairs detection performance in a different modality. In the first experiment the visual awareness threshold for neutral material was raised by simultaneous auditory presentation of emotional words. This result supports the hypothesis that threshold changes induced by emotional stimulation are mediated centrally. In the second experiment a similar effect was obtained when the experimental roles of the two modalities were reversed. An analysis of the effect in terms of the parameters of Signal Detectability Theory indicates that it is mediated by a lowering of the sensitivity of the detection mechanism. This may be caused either by attenuation of incoming signals, or by an increase in the level of “noise” against which the signal is received.

The effect of set on the two-point tactual threshold

This experiment studies the influence of set on the two-point tactual threshold. The two-point limen (critical stimulus) was determined along the mid-longitudinal line of both volar and dorsal surfaces of the right forearms of seven university students. Test-stimuli were selected at 3 mm. steps both up and down from each of the critical stimuli. Each of these test-stimuli was presented separately, the critical stimulus being interpolated 30 times in each test of the series. The proportions of two-point and one-point responses to the critical stimulus were then determined again in a control series. It was found that, as the test-stimulus deviated in the positive direction from the critical stimulus, the proportion of two-point responses to the critical stimulus increased, reached a maximum and then began to decline. A similar rise and fall in one-point responses were found in the opposite direction. The results were explained by Adaptation Level Theory.