In the present study two separate stimulus–response compatibility effects (functional affordance and Simon-like effects) were investigated with centrally presented pictures of an object tool (a torch) characterized by a structural separation between the graspable portion and the goal-directed portion. In Experiment 1, participants were required to decide whether the torch was red or blue, while in Experiment 2 they were required to decide whether the torch was upright or inverted. Our results showed that with the same stimulus two types of compatibility effect emerged: one based on the direction signalled by the goal-directed portion of the tool (a Simon-like effect as observed in Experiment 1), and the other based on the actions associated with an object (a functional affordance effect as observed in Experiment 2). Both effects emerged independently of the person's intention to act on the stimulus, but depended on the stimulus properties that were processed in order to perform the task.

The Simon effect consists of a faster and a more accurate performance when spatial responses correspond to irrelevant-spatial stimuli than when they do not. The time course of the Simon effect was investigated using centrally presented conventional signals (arrows and spatial words) conveying spatial information through iconic-symbolic (Experiments 1 and 2) and semantic (Experiment 3) codes. Time-demanding object-inherent and semantic spatial codes were generated for arrows and words, respectively. This resulted in Simon effects increasing in size across increasing response times (RTs). However, different onsets of the Simon effect were displayed across RT distributions. For arrows, the Simon effect was already significant at the fastest RT intervals, providing clear evidence that they are distinctively more effective directional indicators compared to words.

The aim of the present study was to investigate the relationship between the affordance effect (i.e., the advantage for responses corresponding spatially with the location of an object's graspable part) and the Simon effect (i.e., the advantage for responses corresponding spatially with stimulus location) and to assess whether they both occur at the response selection stage. In two experiments participants were required to respond according to the vertical orientation (upward or inverted) of photographs of graspable objects, located to the left or right of fixation, with their handles oriented to the right or left. In Experiment 1 the response was a buttonpress; in Experiment 2 was a reaching movement. Our results showed that both Simon and affordance effects emerged in response times but not in movement times. In Experiment 1, the two effects did not interact, whereas a clear interaction emerged in Experiment 2. These results seem to suggest that the interaction between Simon and affordance effects may depend on the type of required action.

The present work set out to test the prediction of the dual-route response selection account of the Simon effect, which maintains that the Simon effect, and its facilitation and interference components, should show up at the response selection stage irrespective of when it takes place during processing. Previous works have shown that in the case of a movement response, two strategies can be adopted for responding. The main difference between these two response strategies consists of when response selection operations take place. The two experiments reported in the present study showed that when response selection operates clearly before movement initiations, the Simon effect shows up in reaction time and not in movement time.