Abstract: The human visual system may retain ancestral mechanisms uniquely dedicated to the rapid detection of immediate and specific threats (e.g. spiders and snakes) that persistently recurred throughout evolutionary time. We hypothesized that one such ancestral hazard, spiders, should be inherently prioritized for visual attention and awareness irrespective of their visual or personal salience. This hypothesis was tested using the inattentional blindness paradigm in which an unexpected and peripheral stimulus is presented coincidentally with a central task-relevant display. Despite their highly marginalized presentation, iconic spiders were nonetheless detected, localized, and identified by a very large proportion of observers. Observers were considerably less likely to perceive 1) different configurations of the same visual features which diverged from a spider prototype, or “template”, 2) a modern threatening stimulus (hypodermic needle) comparable in emotional salience, or 3) a different fear-irrelevant animal (housefly). Spiders may be one of a very few evolutionarily-persistent threats that are inherently specified for visual detection and uniquely “prepared” to capture attention and awareness irrespective of any foreknowledge, personal importance, or task-relevance.
Alex’s Notes: I want to start by having us clear our minds and just think for a moment. Being able to stay focused on a task is desirable, especially in a world full of potential distractions. Yet some distractions may be important while others obviously are not. The authors of the study at hand, Joshua New & Tamsin German, speculate that
“The visual system may be inherently prepared to orient attention to a third class of events – specific types of objects that have been of recurring and immediate importance over evolutionary time.”
To elaborate, consider our primate kin who spend their lives in the forests and trees. A great threat to them was snakes, and the coexistence of these old world apes with snakes drove strong evolutionary pressures for the ability of the apes to detect snakes pre-attentively. This is in contrast to other species that developed venom resistance, likely because the snakes were not constantly “after” the apes, making the bites rare and it being more advantageous to simply avoid the problem.
Now consider our ancestors. We abandoned the trees for the grasslands long before finally leaving Africa, making a threat unique to us the spider. For instance, the black widow (Latrodectus) populated Africa long before we did. These highly venomous spiders could easily cause problems for our survival, and even when the spider bites weren’t fatal it would often leave the victim incapacitated for days to weeks. And yet, avoiding these little suckers is not difficult provided you notice them in time. Of course that is the problem; these spiders are small and dark and like to hide. As New & German point out,
“Detection, therefore, is the critical arbiter of success in such encounters – any improvements to the sensitivity, vigilance, reliability, and speed of faculties for their detection would have been of significant selective advantage.”
As we are continuing to realize, the modern human (i.e. us) is not very far removed from our ancestors. It stands to reason that the ability to spot and notice these ancestral threats would still preserve today, despite their infrequency and inconsequentiality with modern medicine. New & Gill aimed to test this hypothesis using the inattentional blindness (IB) paradigm where an unexpected stimulus is presented randomly into the peripheral vision of subjects focused on a separate, central task. In other words, it would be like an image suddenly showed up in my peripheral vision while I am busy focusing on writing this sentence. The reason for using the IB task is straight-forward: it emulates the conditions under which our ancestors typically encountered spiders; without foreknowledge, warning, or task-relevance.
The defining visual configuration of spiders appears to be the radiation of multiple segments from a central mass point with “legginess” being the most frequently reported frightening feature by spider-fearful individuals. This, a “spider template” is one that encompasses a range of configurations in which spiders naturally appear – including curled up and “rectilinear” (composed entirely of straight lines and rectangles comparable to the sizes and lengths of the original curvilinear features).
“First and foremost, this study demonstrated that spiders – a model instance of an evolutionarily-persistent threat – are uniquely capable of capturing observers’ visual attention and awareness. Without any forewarning and despite their marginalized presentation, the prototypical spiders were detected, located, and identified by a majority of participants in both the original experiment and replication.”
Another interesting finding was that the likelihood that a subject detected, located, or identified the spiders was not related to how much fear they felt for it. Taken together with the above, the results emphasize why we cannot overlook our ancestry from a unique perspective. We are very much as human today as we were millions of years ago.