In the visual pure task, the S1 was a line-drawing depicting a monitor and the S2 consisted of purely visual inputs. In the auditory pure task, the S1 was a line-drawing depicting headphones and the S2 consisted of purely auditory

inputs. Global switch costs (also referred to as mixing costs), reflecting the cost related to performing two tasks instead of one task, were obtained by comparing repeat trials in mixed blocks vs. pure task blocks. The auditory part of the bisensory S2 stimulus consisted of two sequentially presented sinusoidal tones (100 ms duration, 10 ms rise and Ku-0059436 fall) with a 5-ms interval between presentations. On non-target trials, the two tones were of identical frequency (2 kHz) and subjects were required to withhold responses when no difference between the tones was detected. On target trials, the two tones presented were of slightly different frequency. One of the two tones was 2 kHz and the frequency separation of the other tone was psychophysically titrated based on each participant’s performance (see ‘Procedure’ below). When participants detected a frequency difference between the pair of tones, they were

instructed to respond with a fast accurate button push. The visual part of the bisensory S2 stimulus consisted of a pair of gabor patches (100 ms duration, 4.8° in diameter, 0.25 cycles per degree) centered 5.2° to the left and right of the fixation cross. On target and non-target trials, respectively, the two patches were of different GSI-IX price and identical orientations. As with the auditory stimuli, the orientation difference between the gabors was psychophysically titrated for each click here participant (see ‘Procedure’ below). The timing of the visual presentation was adjusted such that the Gabors appeared coincident with the second tone of the pair rather than the first. The likelihood of receiving a target stimulus within the cued modality was set at 50%. The stimulus-onset asynchrony between the cue and the imperative stimulus (i.e. the S1–S2 period) was 1350 ms. A black fixation cross (subtending 0.3° vertically and horizontally) was presented in the center of the monitor throughout testing. The inter-trial

interval (the S2–S1 period) was randomised ranging from 2000 to 3000 ms during which the fixation cross remained on the screen. Participants were seated in a double-walled, darkened, sound-attenuated, electrically-shielded booth [International Acoustics Company (IAC), Bronx, NY, USA]. Visual stimuli were presented on an LCD monitor positioned 100 cm from the participant. Auditory stimuli were binaurally presented over a pair of headphones (Sennheiser, model HD 555). Stimuli were delivered using Presentation software (Neurobehavioral Systems, Albany, CA, USA). The sound pressure level was set to a level reported as comfortable by the participant at the beginning of testing, and held constant from then onwards. All participants underwent a staircase procedure at the beginning of testing for each of the two tasks.