Spiders appear to move faster than non-threatening objects regardless of one's ability to block them

• We examined perceived speed of spiders, ladybugs, and balls.
• Spiders were perceived to move faster than ladybugs and balls.
• Decreasing the perceiver's ability to block the object made the object look faster.
• Blocking ability and object type made independent contributions to speed perception.

We examined whether perception of a threatening object – a spider – was more accurate than of a non-threatening object. An accurate perception could promote better survival than a biased perception. However, if biases encourage faster responses and more appropriate behaviors, then under the right circumstances, perceptual biases could promote better survival. We found that spiders appeared to be moving faster than balls and ladybugs. Furthermore, the perceiver's ability to act on the object also influenced perceived speed: the object looked faster when it was more difficult to block. Both effects – the threat of the object and the perceiver's blocking abilities – acted independently from each other. The results suggest effects of multiple types of affordances on perception of speed.