Is 'heavy' up or down? Testing the vertical spatial representation of weight.

Smaller numbers are typically responded to faster with a bottom than a top key, whereas the opposite occurs for larger numbers (a vertical spatial-numerical association of response codes: i.e. the vertical SNARC effect). Here, in four experiments, we explored whether a vertical spatial-magnitude association can emerge for lighter vs. heavier items. Participants were presented with a central target stimulus that could be a word describing a material (e.g. 'paper', 'iron': Experiment 1), a numerical quantity of weight (e.g. '1 g', '1 kg': Experiment 2) or a picture associated with a real object that participants weighed before the experiment (Experiments 3a/3b). Participants were asked to respond either to the weight (Experiments 1-3a) or to the size (i.e. weight was task-irrelevant; Experiment 3b) of the stimuli by pressing vertically placed keys. In Experiments 1 and 2, faster responses emerged for the lighter-bottom/heavier-top mapping-in line with a standard SNARC-like effect-whereas in Experiment 3a the opposite mapping emerged (lighter-top/heavier-bottom). No evidence of an implicit weight-space association emerged in Experiment 3b. Overall, these results provide evidence indicating a possible context-dependent vertical spatial representation of weight.