Distinct perceptual grouping pathways revealed by temporal carriers and envelopes

S. E. Guttman, L. A. Gilroy, and R. Blake (2005) investigated whether observers could perform temporal grouping in multi-element displays where each local element was stochastically modulated over time along one of several potential dimensions--or "messenger types"--such as contrast, position, orientation, or spatial scale. Guttman et al.'s data revealed that grouping discards messenger type and therefore support a single-pathway model that groups elements with similar temporal waveforms. In the current study, we carried out three experiments in which temporal-grouping information resided either in the carrier, the envelope, or the combined carrier and envelope of each messenger's timecourse. Results revealed that grouping is highly specific for messenger type if carrier envelopes lack grouping information but largely messenger nonspecific if carrier envelopes contain grouping information. These imply that temporal grouping is mediated by several messenger-specific carrier pathways as well as by a messenger-nonspecific envelope pathways. Findings also challenge simple temporal-filtering accounts of perceptual grouping (E. H. Adelson & H. Farid, 1999).