Seeing the world through…the same lens: do rats perceive the way we do?
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Have you ever found yourself watching a movie or TV show where the sound was out of sync with the visuals, and you were annoyed only to realize a few minutes later that you don’t even notice the lag anymore? One explanation might be that the audio was fixed, but the more likely explanation is that your brain started to compensate and adjust for the lag. This is one of the many examples of the malleability of our perception and how our perception shifts to accommodate for our environment.
How we, as humans, perceive the world is dependent upon our different senses and rarely, are these senses presented in solitary. Rather, the multisensory nature of the world provides us with a constant influx of different sensations that must be combined in our brains to form our perception. But is this skill exclusive to humans? Typically, this complex phenomenon of multisensory perception is one that we think differs between humans and animals.
However, the author, Mohammed Al-youzbaki, states that “when it comes to neuroscience, a lot of the times we separate ourselves from animals thinking we are special, [and that] we perceive things differently… but seeing how [the animals’] perception shifts predictably exactly like humans, it tells us that they have a similar structure to their perception”.
Therefore, to confirm whether rats have similar perception to humans, Al-youzbaki and colleagues studied the similarities between human and rat audiovisual temporal perception. Audiovisual temporal perception refers to our perception of auditory and visual stimuli depending on when the stimuli were presented relative to the other. This temporal aspect of audiovisual perception is especially important to study because there is a discrepancy between the speed at which sound and light travel and, physiologically, there is a discrepancy between how fast they are processed in the brain. Consequently, there must be sophisticated systems in the brain that combine, or separate, these auditory and visual signals in order to provide us with an accurate perception of the world around us.
In their paper, the researchers use two tasks that have previously been used to measure audiovisual temporal perception: the temporal order judgement (TOJ) task and synchrony judgement (SJ) task. In the TOJ task, participants must judge whether a light flash or a sound was presented first, while in the SJ task, they must determine whether the light and sound were presented synchronously or asynchronously. During the task, the lights and sounds are presented at various timing delays (e.g., the light may come 200ms before the sound in one trial and come 100ms before the sound in the next) to determine the window of time and tolerance for perceiving the stimuli as a single event. Research has revealed that rats performing these tasks do indeed show similar behavioural performance to humans who perform the same task.
In the current study, researchers wanted to confirm whether rats exhibit the same hallmarks of audiovisual temporal perception. If you remember the example given earlier, out of sync sounds and visuals typically become less noticeable over time. Well, this perceptual recalibration is actually one hallmark of audiovisual temporal perception and, turns out, rats are able to do this too. The researchers found that rats passively exposed to asynchronous auditory- or visual- leading stimuli shifted their perception of synchrony towards the leading side, similar to how our perception adjusts to match the sound and visuals of the movie or TV show.
Interestingly, this recalibration can also occur extremely rapidly, which allows us to benefit immediately instead of having to wait a few minutes for our brains to adjust. In the current paper, the researchers show, again, that rats have the ability to rapidly recalibrate similar to humans. They are able to shift their perception on a trial-by-trial basis where the previous trial immediately influences their perception of synchrony on the next trial.
Lastly, from previous research, we know that our perception can change based on different external conditions. For example, our perception is likely to shift based on changes in the signal-to-noise ratio – a measure comparing the level of desired signal to the level of background noise. In the study, researchers used the presence of background noise to change the signal-to-noise ratio of the auditory stimulus and found that, as predicted, there was a preferential impairment in the rats’ ability to accurately judge the temporal order when an auditory stimulus was presented before a visual.
Therefore, by determining that rats’ perception can shift based on previous sensory experience and that their perception changes in a predictable manner, the study reveals that rats’ audiovisual temporal perception is similar to humans.
“Logically, it makes sense that their perception is similar, but now we have tools to prove or demonstrate that it actually is” – Mohammed Al-youzbaki.
Original Article: Al-youzbaki, M. U., Schormans, A. L., & Allman, B. L. (2023). Past and present experience shifts audiovisual temporal perception in rats. Frontiers in Behavioral Neuroscience.