I am deathly afraid of brown recluses like the one in the picture, the nasty little bugger. I never put on a pair of jeans without shaking them first, ’cause they like warm, dark places (and I know someone who was bitten by one hiding in her jeans), and when I recently found one in my medicine cabinet, I strongly considered moving. Other spiders? Who cares? Some of them are even kind of cute. But if you want to see me jump, show me a brown recluse in a jar (if you want to see me run, open the jar).
I tell you this to assure you of my deep, visceral appreciation of the need for an innate spider detection mechanism, even if I’m entirely agnostic about the existence of one. As a result of this appreciation, I was intrigued, if a little amused, when I saw that there is a brief article by Rakison and Derringer in press in the journal Cognition titled, “Do infants possess an evolved spider-detection mechanism?” (which you can read here, no subscription required).
The paper describes three “preferential looking” studies designed to test for the existence of the “Evolved spider-detection mechanism.” Preferential looking studies are based on a simple principle: infants tend to look longer at stuff that interests them. So if you show an infant a bright, noise-making toy on one side of a computer screen, and your tax returns on the other, chances are they’re going to look longer at the toy. It’s a simple, effective, and widely used paradigm in infant research. The idea, then, is that if infants have an “evolved spider-detection mechanism” (I just like the ring of that), they’re going to look longer at spiders than at other stuff. The problem, of course, is figuring out the relevant “other stuff,” and it turns out that this study may not covered all of the “other stuff” bases, but I’m getting ahead of myself.
In their first study, Rakison and Derringer showed infants between 4 1/2 and 5 1/2 months old the three figures pictured above (from their Figure 1a, p. 3) for up to two minutes (they stopped the trial if the infants looked away from the screen for 5 seconds prior to the two-minute mark), and timed how long they looked at each figure. In case the figure captions aren’t clear, the left-most figure is a (decidedly un-brown-recluse-like) “schematic spider,” the one in the middle is a spider reconfigured by turning the legs around, and the one on the right is a spider with all its features thrown about in a semi-random order (or ” completely scrambled,” as an egg, or a smushed brown recluse). And consistent with the hypothesis that infants have an innate spider detection mechanism, infants looked longer at the schematic spider (mean = 24.1 seconds) than at the “reconfigured” (m = 15.5 seconds) or “scrambled” (m = 17.3 seconds) spiders.
In their second study, they presented infants with similar figures, but this time the spiders’ bodies were rectangular (making them look like spiders from an old Atari 2600 video game), instead of like the curved bodies of actual spiders. Since in this experiment, even the “schematic spiders” didn’t look like real spiders, Rakison and Derringer predicted that infants would look at all three for about the same amount of time, and they did. This suggests it’s not just the configuration, but the spider-likeness of the figures in Experiment 1 that caused infants to look longer.
The third study used a slightly different method. As I said above, the preferential looking paradigm utilizes infants’ tendency to look longer at stuff they find interesting to determine what it is that infants find interesting. It turns out that if you have infants look at the same thing for a while, they get bored with it, and look longer at new stuff. This is called habituation, and it’s a great way to study things like infant categorization, to give one example. If you present infants with a bunch of different examples from the same category, and then with a new example from that category and an example from a different category (to which they haven’t been habituated), and they look longer at the latter, you can conclude that they’ve correctly categorized the new example of the habituated category. So habituation is a really powerful tool.
Rakison and Derringer utilized habituation by showing infants several examples of real spiders (in color photos, none of which were of brown recluses, but one of which was of a black widow… yuck), and then presenting them with the three figures used in their first experiment (the figures presented above). They argue that if, when presented with the schematic, reconfigured, and scrambled spiders after being habituated to real spiders, infants look longer at the reconfigured and scrambled spiders (implying that they consider the schematic spider old and boring now), it will suggest that they are generalizing from real spiders to the schematic spider. This in turn would imply that the infants have a “perceptual template” for spiders that serves the “evolved spider-detection mechanism.”
And that’s what they found. The infants only looked at the schematic spider for 6.7 seconds on average, while the mean looking times for the reconfigured and scrambled spiders were 12.1 and 13.4 seconds respectively. Thus the infants were able to generalize from the real spiders to the schematic one, and found it boring as a result.
Do infants have an “evolved spider-detection mechanism,” then? Eh. These studies are suggestive, but there’s a glaring alternative explanation. We already have a bunch of evidence that humans have an innate agency-detection mechanism (there are even books based on that research). If you look closely at the figures above, only one of them looks like it could really be an animate agent: the shematic spider. The reconfigured one might be a dead spider, and the scrambled one might be a spider on the bottom of someone’s shoe, but neither of them looks like it’s a possible agent. So it’s not really surprising that infants look longer at the a agent than the non-agents. So the study lacks the proper controls that would allow it to conclude that infants really do have an innate spider-detection mechanism. To draw that conclusion, you’d need to pit images of spiders (schematic or otherwise) against other, perhaps harmless agents (say, bunny rabbits, as long as they’re not from Caerbannog).
UPDATE: I neglected to mention a 4th study in the paper, which, in a comment, Wes Anderson suggests addresses my point about the lack of proper control. The fourth experiment is pretty much like the first, but instead of looking at spiders, infants looked at a schematic, reconfigured, and scrambled drawings of flowers. This experiment is meant to control for the possibility that infants are looking longer at schematic spiders because they are biologically plausible, while the reconfigured and scrambled spiders are not. Turns out, they look the same at all three, suggesting that it’s not just biological plausibility that causes them to look longer at the schematic spiders.
I left this study out, perhaps unwisely, because I think it’s utterly pointless. The proper control is another animate agent, not a flower (which is clearly not an animate agent), and if “biological plausibility” is a concern, then you can use a biologically plausible drawing of another type of agent. Until someone does a study with that control, all the present studies have shown is that infants find agents more interesting than non-agents, which is something we already knew.