Spatial response codes in the representation of time

One of the most ubiquitous attributes of our external and internal world is the temporal duration of the events that populate it. Yet time is an elusive phenomenon that is difficult to grasp with our senses. There is evidence on how the cognitive system represents such an abstract concept as time. In particular, there is a family of spatio-temporal congruency effects which demonstrate that spatial representations often lie beneath temporal ones, while the converse is not necessarily true. For instance, individuals who have been exposed to left-to-right orthographic systems are better at judging short durations or words referring to the past with their left hand, and long durations or future-related words with their right hand, than vice versa. A first control experiment excludes the possibility that this phenomenon could be due to a bigger temporal preparation effect (shorter FPs for longer durations) for the right hand than for left one. Other alternative interpretations concerning manual or hemispheric asymmetries are excluded on the basis of empirical evidence that shows how this spatial-temporal congruency effect occurs for accuracy when the responding hands are crossed and again for speed when two fingers of the same hand are used for responding. This series of experiments suggests that time, similarly to other ordered sequences, is represented under certain circumstances by means of a spatial reference frame that influences motor performance: a mental line running from left to right. A final study tested, by means of Event-related Potentials (ERPs), how this hypothesized mental time line could dynamically pre-activate a corresponding spatial response code from left to right. In congruent conditions (short-left/long-right), a negative-going ERP component developed over the right motor scalp region around the short duration, suggesting an early pre-activation of left-hand responses. This negativity gradually moved to the left motor region towards the long duration, compatibly with a pre-activation of right hand responses. Pre-activations in the opposite direction, however, were not present for the incongruent conditions. These results confirm that, in such tasks, elapsing time is represented from left to right, and this representation generates corresponding response codes which bias behavior. More generally, the studies reviewed here represent multifaceted contributions to the hot debate on how mental and neural representations of abstract concepts that cannot be directly experienced through our senses may partially rely on our richer perceptual and motor representations.