Models of substitution masking E ndel Põder Institute of Psychology, University of Tartu, Estonia

1. ECVP 2011, August 28 – September 1, Toulouse, France Models of substitution masking Endel PõderInstitute of Psychology, University of Tartu, Estonia E-mail: endel.poder@ut.ee Background Substitution masking Enns and Di Lollo (1997) found that a visual target can be strongly masked by just four dots presented after the target. A necessary precondition was unfocused attention. Di Lollo, Enns & Rensink (2000) demonstrated a similar type of masking when the masking dots were turned on simultaneously with the target but remained visible for some time after the target termination (common-onset masking). Unfocused attention was warranted by distracting objects. Computational Model of Object Substitution (CMOS) Di Lollo et al (2000) proposed that substitution masking reflects a reentrant hypotheses-testing process in vision. They presented a quantitative model (CMOS) that should simulate this reentrant hypotheses-testing. The new model: Similar to CMOS, but with a more realistic mechanism of attention. Two attentional episodes in each trial. At the beginning, attention is divided between all objects in a display. The time of focusing of attention is independent of set-size. • Unselective stage:d’ dependent on set-size, independent on mask duration • Selective stage:d’ dependent on mask duration (function estimated from the data), independent of set-size. Totald’ This study I evaluate the assumptions of the Di Lollo et al (2000) model and its supposed relationship with reentrant processing, and test an alternative model for substitution masking data. Probability correct Fit to the experimental data from Di Lollo et al (2000) R2=0.99 (cf. CMOS, R2=0.93) 1. CMOS as an attentional gating model There are two main equations for transformation of signals from target, masker and noise: (1) (2) Substituting Wj(k-1) in equation (1) with equation (2) transforms this part of the model into a single equation This is just an integrating circuit (low-pass filter) applied to input signals! Additional component: delay of focusing of attention, proportional to set-size Probability of correct recognition is determined by the target signal energy relative to the total signal energy at the moment of arrival of attention. The low-pass input filter together with the attentional delay form a simple attentional gating model (Sperling & Weichselgartner, 1995). Conclusion 1: CMOS is a version of attentional gating model. It does not contain anything related to reentrant hypotheses-testing. Estimated d’ of selective stage 2. New model for substitution masking A problem with CMOS CMOS predicts a particular form of the mask duration and set-size interaction. Because the time of deployment of attention is supposed to be proportional to the set-size, the breakpoints of the masking curves should be shifted along the x-axis, in proportion to the set-size. This is not observed in experimental data. Furthermore, there is no good reason for the delay proportional to the set-size. Typical CMOS predictions Conclusion 2: The new attentional gating model fits the data better than CMOS. References Di Lollo, V., Enns, J.T., & Rensink, R.A. (2000). Competition for consciousness among visual events: The psychophysics of reentrant visual processes. Journal of Experimental Psychology: General, 129 (4), 481-507. Enns, J.T., & Di Lollo, V. (1997). Object substitution: A new form of visual masking in unattended visual locations. Psychological Science, 8, 135-139. Sperling, G., & Weichselgartner, E. (1995). Episodic theory of the dynamics of spatial attention. Psychological Review, 102, 503-532.