Independent sampling vs interitem dependencies in whole report processing:Contributions of processing architecture and variable attention

All current models of visual whole report processing assume perceptual inde pendence among the displayed items in which the perceptual processing of in dividual items is not affected by other items in the display. However, mode ls proposed by Townsend (1981, Acta Psychologica 47; 149-173), Shibuya and Bundesen (1988, Journal of Experimental Psychology: Human Perception and Pe rformance 14, 591-600), and Bundesen (1990, Psychological Review 97, 523-54 7) contain postperceptual buffers that must predict negative dependencies. The perceptual-independence assumption forms what we term the modal model c lass. A recent example of a model that assumes perceptual independence is t he independent Sampling Model of Loftus, Busey, and Senders (1993, Percepti on and Psychophysics 54, 535-554). The fundamental independence assumption has only been directly tested once before, where tests revealed no dependen cies except those produced by guessing. The present study tests tile indepe ndence assumption using several different statistics and, contrary to most extant models of whole report, finds significant positive dependence. Poiss on models do predict a positive dependence and we develop a succinctly para meterized version, the Weighted Path Poisson Model, which allows the finish ing order to be a weighted probabilistic mechanism. However, it does not pr edict the data quite as well as a new model, the Variable Attention Model, which allows independence within trials (unlike the Poisson models). This m odel assumes that attention (or, potentially, other aspects such as signal quality) varies widely across trials, thus predicting an overall positive d ependence. Intuitions For and against the competing models are discussed, I n addition, we show, through mimicking Formulae, that models which contain the proper qualitative type of dependence structure can be cast in either s erial or parallel form. (C) 2001 Academic Press.