Target enhancement and distractor inhibition affect transitory surround suppression in dual tasks using multiple rapid serial visual presentation streams

Few studies have investigated the interaction between temporal and spatial dimensions on selective attention using dual tasks in the multiple rapid serial visual presentation (RSVP) paradigm. A phenomenon that the surround suppression in space changes over time (termed transitory surround suppression, TSS, in the present study) has been observed, suggesting the existence of this time-space interaction. However, it is still unclear whether target enhancement or distractor inhibition modulates TSS. Four behavioural experiments were conducted to investigate the mechanism of TSS by manipulating the temporal lag and spatial distance factors between two targets embedded in six RSVP streams. The TSS effect was replicated in a study that eliminated confounds of perceptual effects and attentional switch (Experiment 1). However, the TSS disappeared when two targets shared the same colour in a between-subjects design (Experiment 2a) and a within-subject design (Experiment 2b), suggesting the impact of target enhancement on TSS. Moreover, the TSS was larger for within-category than for between-category distractors (Experiment 3), indicating the impact of distractor inhibition on TSS. These two influences on TSS under different processing demands of target and distractor processing were further confirmed in a skeletal design (Experiment 4). Overall, combinative effects of target enhancement and distractor suppression contribute to the mechanisms of time-space interaction in selective attention during visual search.