Differences in perceptual masking between humans and rats

Abstract

Introduction The perception of a target stimulus can be impaired by a subsequent mask stimulus, even if they do not overlap temporally or spatially. This “backward masking” is commonly used to modulate a subject's awareness of a target and to characterize the temporal dynamics of vision. Masking is most apparent with brief, low‐contrast targets, making detection difficult even in the absence of a mask. Although necessary to investigate the underlying neural mechanisms, evaluating masking phenomena in animal models is particularly challenging, as the task structure and critical stimulus features to be attended must be learned incrementally through rewards and feedback. Despite the increasing popularity of rodents in vision research, it is unclear if they are susceptible to masking illusions. Methods We characterized how spatially surrounding masks affected the detection of sine‐wave grating targets. Results In humans (n = 5) and rats (n = 7), target detection improved with contrast and was reduced by the presence of a mask. After controlling for biases to respond induced by the presence of the mask, a clear reduction in detectability was caused by masks. This reduction was evident when data were averaged across all animals, but was only individually significant in three animals. Conclusions While perceptual masking occurs in rats, it may be difficult to observe consistently in individual animals because the complexity of the requisite task pushes the limits of their behavioral capabilities. We suggest methods to ensure that masking, and similarly subtle effects, can be reliably characterized in future experiments.

Assessing tests of animal consciousness

“…I do not want to minimize the methodological challenges involved in applying masking paradigms to other mammals, let alone invertebrates. However, such paradigms have at least been transferred to rats and it seems that masking effects indeed occur in rats (Dell et al 2019). In addition, analogous masking effects are also found in other sensory modalities, e.g.…”

Rats spontaneously perceive global motion direction of drifting plaids

“…Assessing such similarity was the ultimate goal of our experiments, since it allowed understanding whether, in the crosspriming condition, the perceived motion direction of the plaids was the global one. Based on previous motion adaptation studies in humans [41] and on former priming/masking experiments carried out in rats [34,[42][43][44], we choose the duration of the prime and of the interstimulus interval (ISI) between prime and target (75 ms each) in the attempt of inducing a strong priming effect-i.e., in the attempt of biasing rats' responses to the target towards the motion direction of the prime.…”

Rats spontaneously perceive global motion direction of drifting plaids

“…Assessing such similarity was the ultimate goal of our experiments, since it allowed understanding whether, in the cross-priming condition, the perceived motion direction of the plaids was the global one. Based on previous motion adaptation studies in humans (Kanai and Verstraten, 2005) and on former priming/masking experiments carried out in rats (Tafazoli et al, 2012;Alwis et al, 2016;Dell et al, 2018Dell et al, , 2019, we choose the duration of the prime and of the inter-stimulus interval (ISI) between prime and target (75 ms each) in the attempt of inducing a strong priming effect -i.e., in the attempt of biasing rats' responses to the target towards the motion direction of the prime.…”