Time pressure affects response precision but not psychological similarity in inferences from multiple features
People excel in categorizations–even under time pressure. We investigated how the human mind copes with time pressure during category inference by comparing three cognitive mechanisms within a framework, in which inferences about new objects are informed by similar previous objects. Specifically, we tested whether time pressure causes people to focus their attention to fewer object features, to respond less precisely, or to simplify the similarity computation by counting the number of differing features between objects but ignoring the precise feature value differences. To this end, we collected experimental data in the domains of categorization and similarity judgments and combined inferential statistics and computational cognitive modeling within the exemplar-similarity framework. In the categorization experiment, participants (N = 61) solved a trial-by-trial supervised, binary category learning task without time pressure, followed by unsupervised transfer categorizations with individually-calibrated time pressure for half the participants (M = 902 ms). The experimental design was optimized in simulations to maximally discriminate between the formal models in the transfer task. The results show that participants categorized the transfer stimuli less consistently with than without time pressure. In turn, we found no credible evidence that time pressure induced an attention focus or a simplified similarity. In the similarity judgment experiment, participants (N = 175) rated on a slider the similarity of various stimulus pairs once without time pressure and once with an individually-calibrated time pressure, manipulated across participants to be either weak (N = 64, M = 2018 ms), medium (N = 55, M = 1225 ms), or strong (N = 56, M = 510 ms). The results corroborate those from the categorization experiment, strongly suggesting that time pressure lowers response precision. Participants’ similarity judgments got more variable with time pressure, plateauing at medium time pressure, with SDs being .13 (no time pressure) < .17 (weak) < .19 (medium) = .18 (strong), signs denote statistical significance in a linear mixed model. In turn, participants’ mean similarity judgments for the stimulus pairs followed the same rank order across all experimental conditions. This strongly suggests that time pressure did not change participants’ similarity judgments qualitatively, as would be expected from an attention focus or a simplified similarity. In sum, we found that cognitive load in similarity-based categorizations and judgments does not necessarily affect computational processes related to attention or psychological similarity, but rather the precision with which people translate their internal beliefs to manifest responses.