Evidence accumulation in temperature perception: Distinct effects of spatial summation and lateral inhibition

Human perception integrates sensory information to form coherent representations of the environment. In thermosensation, spatial summation and lateral inhibition influence the intensity of cold and warm sensations, but it remains unclear how these processes influence perceptual decisions. One proposed account is that thermosensory judgements rely on evidence accumulation, in which sensory information is sampled sequentially and integrated over time until a decision is reached. To examine how spatial summation and lateral inhibition influence this process, we developed two thermosensory discrimination tasks in which participants classified stimuli as cold or warm during either dynamic temperature changes or the presentation of specific target temperatures (20 °C and 42 °C). We systematically manipulated the spatial characteristics of the stimuli, varying the total stimulated skin area to investigate spatial summation, and the distance between stimulation zones to examine lateral inhibition. Generalized linear modeling revealed that spatial summation exerted modality- and task-dependent effects on both response times and perceived intensity. In contrast, lateral inhibition had limited and inconsistent effects, emerging only in intensity ratings under target temperature conditions. Drift diffusion modeling demonstrated that larger stimulation areas reliably accelerated evidence accumulation across both modalities and stimulation dynamics, whereas greater spatial distance selectively increased drift rates during dynamic warm stimulation. Bias estimates differed by task and modality, with a consistent bias toward the cold boundary during dynamic warm trials. These findings suggest that thermosensory decisions are shaped by spatial integration processes that modulate evidence accumulation and decision bias. Our results extend the evidence accumulation framework to temperature perception.