Search for feature and for relative position: measurement of capacity limitations

Palmer and his associates (Palmer, Ames & Lindsey (1993). Journal of Experi mental Psychology: Human Perception and Performance, 19, 108-130; Palmer (1 994). Vision Research, 34, 1703-1721) have confirmed that searches for simp le feature targets are not limited by perceptual processing capacity and th e effect of set size on performance can be accounted for by integration sta ge processes only. In this study I used a similar difference threshold meth od with target and distracter stimuli defined by the relative position of t heir elements (line drawings of bisected squares) and found clear capacity limitations. Feature search condition, however, with nearly comparable bise cted square stimuli did replicate the results of Palmer and associates. Thi s experiment demonstrates that a search for targets defined by relative pos ition in the set of line drawing type of stimuli is fundamentally different from a search for more simple (feature) stimuli and may conform to a stric t capacity limited model. (C) 1999 Elsevier Science Ltd. All rights reserve d.