The coding of repetitions and alternations in action sequences: spatial or relational?

We used variants of the Simon task to investigate whether repetitions and alternations in short keypress sequences are represented by spatial or relational codes. With spatial coding, either absolute or relative location would be used for coding the second response in a sequence. With relational coding, the second response would be coded in terms of a non-spatial relation to the first one (e.g., left response—same response, for a repetition). In three experiments with different imperative stimuli, we compared Simon effects across three experimental conditions, a single-response condition, a response-repetition condition (each stimulus required two keypresses on the same side, e.g., left–left), and a response-alternation condition (each stimulus required a keypress on each side, e.g., left–right). When compared to the single-response condition, spatial coding of the second response should modulate the Simon effect (i.e., response conflict) in selecting the first response because spatial coding of the second response produces additional dimensional overlap of stimulus and the second-response code. We observed Simon effects in the response times of first responses in each condition, and they increased in the response-alternation condition, but not in the response-repetition condition. The findings suggest relational coding of response repetitions, and spatial coding of response alternations.