Additive factors do not imply discrete processing stages: a worked example using models of the stroop task.

Tom Stafford,Kevin N Gurney

doi:10.3389/fpsyg.2011.00287

Abstract

Previously, it has been shown experimentally that the psychophysical law known as Piéron’s Law holds for color intensity and that the size of the effect is additive with that of Stroop condition (Stafford et al., 2011). According to the additive factors method (Donders, 1868–1869/1969; Sternberg, 1998), additivity is assumed to indicate independent and discrete processing stages. We present computational modeling work, using an existing Parallel Distributed Processing model of the Stroop task (Cohen et al., 1990) and a standard model of decision making (Ratcliff, 1978). This demonstrates that additive factors can be successfully accounted for by existing single stage models of the Stroop effect. Consequently, it is not valid to infer either discrete stages or separate loci of effects from additive factors. Further, our modeling work suggests that information binding may be a more important architectural property for producing additive factors than discrete stages.

Highlights

Much progress has been made on the neurological and theoretical foundations of simple perceptual decisions (Gold and Shadlen, 2001; Platt, 2002; Opris and Bruce, 2005)
In the current paper we show that the assumptions of the Additive Factors Method are untenable, using as a worked example decision making in a specific cognitive task
This work throws into contrast both models of optimal decision making and a longer tradition of experiments informed by the Additive Factors Method

Summary

INTRODUCTION

Much progress has been made on the neurological and theoretical foundations of simple perceptual decisions (Gold and Shadlen, 2001; Platt, 2002; Opris and Bruce, 2005). Note that for the single stage model with unlocked inputs the result for the conflict condition at the lowest color intensity is not shown This is because at this point the model stops predicting the EXTENDING CONTINUOUS PROCESSING MODELS OF THE STROOP TASK In the original model the word and color information is represented by 0 or 1 values on the input layer Stage is a rise-to-threshold process where the time-to-completion is defined by thresh/intensity where, in this case, thresh = 10 and intensity reflects the stimulus intensity (i.e. color saturation here) and is taken as the values 0.2, 0.4, 0.6, 0.8, or 1.0 This stage is based on evidence accumulation models of perceptual decision making (Ratcliff, 1978; Usher and McClelland, 2001; Bogacz et al, 2006). Simulations involving architectures with two clearly discrete stages of processing show that such architectures can produce additive factors, as has been traditionally assumed, FIGURE 7 | Simulation data for two stage model with unlocked inputs

DISCUSSION

GENERAL DISCUSSION