Number-Time Interaction: Search for a Generalized Magnitude System

Abstract

Space, time, and number are fundamental to human cognition. The mental representations on these entities are crucial for planning and decision-making. In our everyday lives, we are always thinking in terms of quantities — how long would we take to reach the workplace, what would be a shorter route to get to a specific store from where we are, how many cupcakes should we prepare for the people we have invited, how do we throw a stone that will dislodge a shuttlecock stuck in the tree, and so on. Even for simple tasks like grasping, reaching, or catching a ball, subtle calculations involving distance, speed, and time are essential. To successfully execute our actions, we need to synchronize these entities efficiently. For example, to grab an object kept on the table, one needs to integrate information from time, space, and number dimensions to evaluate the obstacles present in that environment and the distance between the object and our body. Further, spatiotemporal integration of information is needed for successful reaching and grasping. Over the last two decades, numerous studies have advanced our knowledge of how humans utilize perceptual information to estimate magnitudes such as space, time, and number. One of the most popular theories of magnitude processing, A Theory of Magnitude (ATOM), suggests that a generalized magnitude system in the brain processes information related to space, time, and numbers. Since these magnitudes are processed by a common magnitude system, they interact with one another. Earlier studies investigating the number-time interaction have provided support to ATOM’s predictions. On the contrary, more recent studies have argued against ATOM and suggested that the cross-dimensional magnitude interactions may emerge from cognitive factors like attention and memory. Such contradicting findings raise a fundamental question as to whether a common magnitude system indeed exists, or such crossdimensional magnitude interactions result from cognitive factors. This is still an unsettled question. In the present thesis, we examine the influence of numerical magnitude on temporal processing in a different experimental setup. More specifically, we investigated whether numerical magnitude affects our temporal experience or simply biases judgment of time. Further, we examined whether large numerical magnitude is always perceived to be longer in time (as predicted by ATOM) or attentional modulation can cause such crossdimensional magnitude interactions. We also tested the generality of the ATOM framework in a cross-modal setting wherein numerical magnitude and temporal information were presented in two different modalities and evaluated ATOM’s prediction in a cross-domain setting. The overall results from the five empirical investigations suggest that the processing of numbers and time may not require to invoke a common magnitude processing system. The cross-dimensional magnitude interactions (in this case, number and time) may emerge from the modulation of attentional mechanisms.