Selective attention is required in tasks that involve the inhibition of competing responses.
When the processing of one stimulus attribute impedes the processing of a simultaneous second stimulus attribute, then cognitive interference occurs. Two experiments were run. In one session, the relevant dimension was numerical size, and in the other session, it was the physical size. Error rates and RT data were analysed. In the first experiment, physical size and numerical distance were manipulated with the purpose of selecting the stimulus features that produced the strongest interference effect.