What should a quantitative model of masking look like and why would we want it?
Gregory Francis · Advances in Cognitive Psychology · 2007
Backward masking refers to reduced visibility of a target stimulus when it is followed by a mask stimulus.The conditions under which masking occurs, and some special properties and uses of backward masking, are well summarized in other papers in this issue (Breitmeyer this volume, Enns, & Oriet, this volume).This paper looks at the status of quantitative models, considers some issues and limitations about such models, and then explores how to proceed in a way that will improve the study and use of backward masking.Studies of masking often vary the timing between the target and mask stimulus.A measure of target visibility plotted against the stimulus onset asynchrony (SOA) between the target and mask is called a masking function.Empirical work typically finds two types of masking functions, referred to as Type A and Type B.A Type A masking function is shown in Figure 1a.The visibility of the target is minimized for common onset of the target and mask (SOA = 0).As the SOA increases, the target becomes more visible.A Type B masking function is shown in Figure 1b.The target is easily visible for common onset of the target and mask stimuli, but becomes less visible as the SOA increases.After reaching a minimum of visibility (maximum of masking) at some intermediate SOA, target visibility increases.Whether Type A or Type B masking is produced depends on the target, mask, experimental task, and conditions of the experiment, as is discussed in other papers in this issue (Breitmeyer this volume, Bridgeman this volume, Herzog, this volume).Scholarly papers on backward masking often describe it as mysterious, paradoxical, or surprising.These claims about backward masking are of two types.First, it is surprising to some researchers that a trailing mask can affect the visibility of the leading target.Indeed, the phenomenological appearance of the target-mask sequence is sometimes that only the mask is presented.This result is surprising for some views of neural processing that supposes information proceeds in a feed forward manner.In some such views, the earlier target information would always be at a neural location where the mask information was not.In such a view, masking requires the mask information to lead ahead in space (or backward in time) to interfere with the target percept.