Comparing Capacity Estimates for Genuinely No-signal vs Target Absent in Systems Factorial Technology

Ideally, the capacity of a single channel in a multichannel system should be unaffected by task type (e.g, logical “AND” vs “OR” tasks). However, Howard et al. (2021) reviewed studies in which capacity estimates for “AND” tasks differ greatly from “OR” tasks. In the classic definition of capacity, the absence of a component is not explicitly considered. They suggest a need to incorporate processing time random variables from the no-signal channels into the capacity formulation. We recently collected data from the standard double factorial paradigm that allows us to evaluate the utility of this modification. In one experiment, observers detected the presence or absence of components in Navon-like stimuli (i.e., global shape is composed of local shapes) for both the “OR” and the “AND” task instructions. Absence of a target feature was the presence of a neutral distractor. Hence, the no-signal channel actually contained shape information. In contrast, a second experiment used complex Gabor patches composed of two sinewave gratings in the same tasks. Hence, the absence of one grating does imply nothing is present on that channel. We show that modifying the classical capacity coefficient to account for empty channels is more effective for Gabor patches when compared to the Navon stimulus example.