Illusory form with inducers of opposite contrast polarity: Evidence for multistage integration

The perception of brightness differences in Ehrenstein figures and of illusory contours in phaseshifted line gratings was investigated as a function of the contrast polarity of the inducing elements. We presented either continuous lines or line-like arrangements composed of aligned dashes or dots whose spacing was varied. Ayes/no procedure was used in which naive observers had to decide whether or not they perceived a brightness difference in a given Ehrenstein figure or an illusory contour in a phase-shifted line grating. The results show that brightness differences are perceived to some extent in Ehrenstein figures with inducers of opposite polarity of contrast; however, the percentage ofyes responses was systematically lower and response times were longer than for figures with inducers of the same polarity. Phase-shifted line gratings with lines of opposite polarity of contrast yielded stronger illusory contours and shorter response times than those with lines of the same polarity. When the sign of contrast was not the same within a given line of induction, neither differences in brightness nor illusory contours were perceived. The results suggest that the mechanisms that lead to apparent differences in brightness are more sensitive to input of the same contrast polarity, the mechanisms generating illusory contours more sensitive to input of opposite polarity. The data are discussed in the light of a multistage approach to illusory form perception and some implications for cortical models of illusory contour integration are discussed.     

CHANGE IN SELF‐IMAGE AND PTSD SYMPTOMS IN SHORT‐TERM THERAPIES WITH TRAUMATIZED REFUGEES

In this study, an attempt was made to evaluate changes in the self‐image of traumatized refugees receiving short‐term psychotherapy. Fourteen clients with war and torture experiences were followed during and after trauma‐focused therapies with self‐rating instruments. Outcome was measured with SCL‐90, measuring overall psychiatric symptoms, and with PTSS‐10, measuring Post‐traumatic Stress Disorder (PTSD) symptoms. Self‐image was measured with Structural Analysis of Social Behavior (SASB). The analyses showed considerable remission of both general psychiatric and PTSD‐related symptoms, but more moderate changes in self‐image aspects. The positive aspect of the self‐image was virtually non‐related to the symptom measures and did not change after the termination of the therapy; the negative aspect of the self‐image was more strongly related to the symptoms and changed mainly on the last measurement occasion, 15 months after the therapy end. When clients with good and poor outcome were compared, it was found that those with good outcome had higher initial levels on both the positive and the negative aspects of the self‐images. This was tentatively interpreted as indicating that clients who had invested more energy in their self‐image were better able to utilize the therapy. Different development in the self‐image for these two groups indicated that for some clients, the treatment process might have entailed too much strain.