Abstract
A dual-task experiment was designed to determine whether attentional effects are modulated by the size of the exogenous cue. A random-dot kinematogram (RDK), containing 100 white dots, was presented in each visual quadrant. In one RDK, the dots moved in a coherent direction for 200 ms. On 50% of the trials, one of the dots in one RDK turned red. Participants reported the direction of coherent motion and the location or absence of the colour probe, and accuracy was measured. In the first experiment the exogenous cue was a luminance-change frame surrounding the RDK, “flashing” for 80 ms. The cue was uninformative for both the location of the coherent motion and the location of the colour probe. A validity effect was found for the motion discrimination, but not probe localisation. In the second experiment, the cue frame only surrounded the central region of the RDK, to spatially match the probe stimulus. The red dot probe was confined to the same central region of each RDK. A validity effect was evident for both tasks. A third experiment was conducted to ensure that the difference between Experiments 1 and 2 was due to the cue, rather than probe location uncertainty. The cue surrounded the RDK as in Experiment 1, but the probe was confined to the central portion of the RDKs as in Experiment 2. As in Experiment 1, there was only a validity effect for the motion discrimination task, confirming that exogenous spatial attention is affected by the size of the cue. These results suggest that the size of the exogenous cue must match the size of the stimulus in order to have an effect.