Nice article Jason. I should start by saying that as a (mostly former) visual neuroscientist, I think that you’ve done quite a good job summarizing the science available in this series of posts, but particularly in these last two posts about time. I have a few comments that I’d like to add.
Before artificial light sources, there weren’t a lot of blinking lights in nature. So although visual processing speed is often measured as CFF, most animals didn’t really evolve to see flickering lights. In fact, I recall that my PhD supervisor Srinivasan did a study where he tried to behaviorally test honeybee CFF—he had a very hard time training them to go to flickering lights (study 1), but had much more success training them to go to spinning disks (study 2). In fact, the CFF of honeybees is generally accepted to be around 200 Hz, off the charts! That said, in an innate preference study on honeybees that I was peripherally involved with, we found honeybee had preferences for different frequencies of flickering stimuli, so they certainly can perceive and act on this type of visual information (study 3).
Even though CFF has been quite widely measured, if you wanted to do a comprehensive review of visual processing speed in different taxa then it would also be worth looking at other measures, such as visual integration time. This is often measured electrophysiologically (perhaps more commonly than CFF), and I expect that integration time will be at tightly correlated with CFF and as they are causally related, one can probably be approximately calculated from the other (I say approximately because neural nonlinearities may add some variance, in the case of a video system it can be done exactly). For instance, this study on sweat bees carefully characterized their visual integration time at different times of day and different light conditions but doesn’t mention CFF.
Finally, I think some simple behavioural experiments could shed a lot of light on how we expect metrics around sensory (in this case visual) processing speeds to be related to the subjective experience of time. For instance, the time taken to make a choice between options is often much longer than the sensory processing time (e.g. 10+ seconds for bumblebees, which I expect have CFF above 100 Hz), and probably reflects something more like the speed of a conscious process than the sensory processing speed alone does. A rough idea for an experiment is to take two closely related and putatively similar species where one had double the CFF of the other, measure the decision time of each on a choice-task to select flicker or motion at 25%, 50% and 100% of their CFF. So if species one has CFF at 80 Hz, test it on 20, 40 and 80 Hz, and if species two has CFF 40 Hz, test it on 10, 20 and 40 Hz. A difference in the decisions speed curve across each animals frequency range would be quite suggestive of a difference in the speed of decision making that was independent of the speed of stimulus perception. The experiment could also be done on the same animal in two conditions where its CFF differed, such as in a light- or dark-adapted state. For completeness, the choice-task could be compared to response times in a classical conditioning assay, which seems more reflexive, and I’d expect differences in speeds here correlate more tightly to differences in CFF. The results of such experiments seem like they could inform your credences on the possibility and magnitude of subjective time differences between species.
Nice article Jason. I should start by saying that as a (mostly former) visual neuroscientist, I think that you’ve done quite a good job summarizing the science available in this series of posts, but particularly in these last two posts about time. I have a few comments that I’d like to add.
Before artificial light sources, there weren’t a lot of blinking lights in nature. So although visual processing speed is often measured as CFF, most animals didn’t really evolve to see flickering lights. In fact, I recall that my PhD supervisor Srinivasan did a study where he tried to behaviorally test honeybee CFF—he had a very hard time training them to go to flickering lights (study 1), but had much more success training them to go to spinning disks (study 2). In fact, the CFF of honeybees is generally accepted to be around 200 Hz, off the charts! That said, in an innate preference study on honeybees that I was peripherally involved with, we found honeybee had preferences for different frequencies of flickering stimuli, so they certainly can perceive and act on this type of visual information (study 3).
Even though CFF has been quite widely measured, if you wanted to do a comprehensive review of visual processing speed in different taxa then it would also be worth looking at other measures, such as visual integration time. This is often measured electrophysiologically (perhaps more commonly than CFF), and I expect that integration time will be at tightly correlated with CFF and as they are causally related, one can probably be approximately calculated from the other (I say approximately because neural nonlinearities may add some variance, in the case of a video system it can be done exactly). For instance, this study on sweat bees carefully characterized their visual integration time at different times of day and different light conditions but doesn’t mention CFF.
Finally, I think some simple behavioural experiments could shed a lot of light on how we expect metrics around sensory (in this case visual) processing speeds to be related to the subjective experience of time. For instance, the time taken to make a choice between options is often much longer than the sensory processing time (e.g. 10+ seconds for bumblebees, which I expect have CFF above 100 Hz), and probably reflects something more like the speed of a conscious process than the sensory processing speed alone does. A rough idea for an experiment is to take two closely related and putatively similar species where one had double the CFF of the other, measure the decision time of each on a choice-task to select flicker or motion at 25%, 50% and 100% of their CFF. So if species one has CFF at 80 Hz, test it on 20, 40 and 80 Hz, and if species two has CFF 40 Hz, test it on 10, 20 and 40 Hz. A difference in the decisions speed curve across each animals frequency range would be quite suggestive of a difference in the speed of decision making that was independent of the speed of stimulus perception. The experiment could also be done on the same animal in two conditions where its CFF differed, such as in a light- or dark-adapted state. For completeness, the choice-task could be compared to response times in a classical conditioning assay, which seems more reflexive, and I’d expect differences in speeds here correlate more tightly to differences in CFF. The results of such experiments seem like they could inform your credences on the possibility and magnitude of subjective time differences between species.