IN EXP. I TEST DISPLAYS CONTAINING THE FORMS A, T, AND U, WERE FOLLOWED BY A RING MASKING STIMULUS AT INTERSTIMULUS INTERVALS (ISIS) OF 0-100 MSEC. A CIRCULAR ARRANGEMENT WAS USED FOR THE TEST-FORM DISPLAYS. IN THE 1-FORM DISPLAYS ONLY A SINGLE FORM WAS PRESENTED, LOCATED IN 1 OF 6 POSSIBLE POSITIONS ON THE CIRCUMFERENCE OF AN IMAGINARY CIRCLE CENTERED ON THE FIXATION POINT. IN THE 6 TEST-FORM CONDITION 6 FORMS WERE PRESENTED, 1 IN EACH OF THE POSSIBLE POSITIONS, AND S WAS TO IDENTIFY THE 1 FORM THAT WAS SUBSEQUENTLY SURROUNDED BY THE MASKING RING. CONTRARY TO N. WEISSTEIN'S (SEE 40:9) FINDINGS, MASKING WAS A MONOTONIC DECREASING FUNCTION OF ISI FOR BOTH 1 AND 6 TEST-FORM DISPLAYS. IN AGREEMENT WITH WEISSTEIN, GREATER MASKING WHICH EXTENDED OVER LONGER ISI VALUES WAS OBTAINED FOR 6 TEST-FORM DISPLAYS. EXP. II REVEALED THAT THIS MORE EXTENSIVE MASKING FOR 6 TEST-FORM DISPLAYS WAS ATTRIBUTABLE TO 2 INDEPENDENT SUMMATIVE PROCESSES: (1) THE IMPAIRMENT IN FORM IDENTIFICATION DUE TO SURROUNDING THE FORM WITH A RING AT SHORT ISIS, AND (2) A DELAYED INDICATOR EFFECT RESULTING FROM THE DELAY OF INFORMATION AS TO WHICH OF THE 6 FORMS S WAS TO IDENTIFY. (PsycINFO Database Record (c) 2006 APA, all rights reserved)