Spatial response-code association for loudness but not brightness

Cognitive associations between stimulus intensity and spatial response codes are thought to influence perceptual discrimination. We examined lateral response-set effects on auditory and visual intensity discrimination in a preregistered study with a large sample (<i>N</i> = 98). Participants responded to loud and bright stimuli using a button located to the left or right of the button used for soft and dim stimuli. In the auditory task, stimulus-response (SR)-mapping affected task-averaged error rates (ERs) but not task-averaged response times (RTs). However, loudness predicted response-side differences in both latency (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mtext>RT</mml:mtext><mml:mtext>Left</mml:mtext></mml:msub><mml:mo>-</mml:mo><mml:msub><mml:mtext>RT</mml:mtext><mml:mtext>Right</mml:mtext></mml:msub></mml:math>) and accuracy (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mtext>ER</mml:mtext><mml:mtext>Left</mml:mtext></mml:msub><mml:mo>-</mml:mo><mml:msub><mml:mtext>ER</mml:mtext><mml:mtext>Right</mml:mtext></mml:msub></mml:math>). By comparison, all tests of brightness discrimination supported the null or were inconclusive. Assessments of cross-modality correlations in SR-mapping effects were also inconclusive. These results replicate prior findings of lateral SR-mapping effects in auditory intensity discrimination and clarify inconsistencies in the visual domain. The lack of SR-mapping effects in brightness discrimination, along with inconclusive cross-modal correlations, challenges the notion of a common spatial processing mechanism for auditory and visual intensity comparison. If such a mechanism exists, its effects on visual judgments appear too subtle to be detected even in a large sample.