The neural signature of magnitude integration between time and numerosity

Abstract

Magnitude dimensions such as time and numerosity are fundamental components of our visual experience, allowing us to understand the environment and interact with it. Different magnitudes are however not processed independently from each other, but show a relationship whereby the perception of one dimension depends on the others (magnitude integration). In this study, we use electroencephalography (EEG) to address whether such integration may arise from a shared brain processing stage where different dimensions are integrated together, or from independent parallel processes interfering with each other. In the experiment, participants judged either the average numerosity or duration of dynamic dot-array stimuli concurrently modulated in both dimensions. First, the behavioural results show a magnitude integration effect in both tasks, with duration affecting the judgement of numerosity and vice versa. The EEG results further show that both numerosity and duration significantly modulate event-related potentials at several distinct latencies. Crucially, however, we identified a significant interaction between numerosity and duration emerging in a specific latency window (360-460 ms) irrespective of the task performed by participants. In this latency window, the modulation of ERPs provided by the interfering magnitude dimension can be predicted by the strength of the behavioural bias. Our results thus support the idea of different magnitude dimensions converging onto a shared perceptual processing stage mediating their integration. Overall, our results demonstrate a clear electrophysiological signature of magnitude integration between numerosity and time, and provide new evidence for a shared representational system encompassing different magnitude dimensions.

The more numerous the longer: how the integration between numerosity and time leads to a common neural response

“…Similarly, our results highlight the role of parietal cortex as the key point of transition between an early encoding stage and a late perceptual and condition-dependent stage of magnitude processing. If confirmed in future studies, this result could potentially explain both the symmetric and the asymmetric perceptual effects of the interaction between time and numerosity [ 4 , 7 , 22 ].…”

Magnitude processing and integration entail perceptual processes independent from the task

“…This view has been however challenged by the idea that biases across magnitudes, and especially space and time, may stem from the linguistic labels assigned to them, and how we conceptualise these dimensions at a cognitive level (“metaphoric theory;” e.g., Casasanto & Boroditsky, 2008). While evidence has now been accumulated against a linguistic/conceptual view of magnitude integration (Cai & Connell, 2015; Togoli, Bueti, et al, 2022; Whitaker et al, 2022), other theories have proposed that magnitudes interact at a more cognitive rather than perceptual level, as a working memory interference (Z. G. Cai et al, 2018), or as a response bias (Yates et al, 2012). Finally, more in line with a perceptual interpretation of the integration effect, it has been recently proposed (Hendrikx et al, 2024; Tsouli et al, 2022) that the interaction could arise from the processing of different dimensions in partially overlapping cortical maps (Fortunato et al, 2023; Harvey et al, 2013, 2015; Hendrikx et al, 2022, 2024; Protopapa et al, 2019), but without involving a common neural code.…”