Knowledge that Transforms

People often make logically sound decisions using explicit reasoning strategies, but sometimes it pays to rely on more implicit "gut-level" intuition. The transitive inference paradigm has been widely used as a test of explicit logical reasoning in animals and humans, but it can also be solved in a more implicit manner. Some researchers have argued that the hippocampus supports relational memories required for making logical inferences. Here we show that the benzodiazepene midazolam, which inactivates the hippocampus, causes profound explicit memory deficits in healthy participants, but enhances their ability in making implicit transitive inferences. These results are consistent with neurocomputational models of the basal ganglia-dopamine system that learn to make decisions through positive and negative reinforcement. We suggest that disengaging the hippocampal explicit memory system can be advantageous for this more implicit form of learning.

The binding of object identity (color) and location in visual short-term memory (VSTM) was examined in 6.5- to 12.5-month-old infants (N= 144). Although we previously found that by age 6.5 months, infants can represent both color and location in VSTM, in the present study we observed that 6.5-month-old infants could not remember trivially simple color-location combinations across a 300-ms delay. However, 7.5-month-old infants could bind color and location as effectively as 12.5-month-old infants. Control conditions confirmed that the failure of 6.5-month-old infants was not a result of perceptual or attentional limitations. This rapid development of VSTM binding between 6.5 and 7.5 months occurs during a period of rapid increase in VSTM storage capacity and just after a period of dramatic neuroanatomical changes in parietal cortex. Thus, the ability to bind features and the ability to store multiple objects may both depend on a process that is mediated by posterior parietal cortex and is perhaps related to focused attention.

Decrements in performance on cognitive tasks resulting from pressure to perform (i.e., choking) are thought to be caused by interference with the ability to use explicit strategies (the distraction theory). This view suggests that pressure should improve performance on tasks for which explicit strategies hamper performance. This hypothesis was tested by giving subjects one of two nearly identical learning tasks, a task that required learning a rule or one that required using a holistic information-integration strategy. Explicit rule use would hurt performance in the latter task. As predicted by the distraction theory, pressure decreased performance on the rule-based task but enhanced performance on the information-integration task.

Recent studies have shown that emotionally significant stimuli are often better identified than neutral stimuli. It is not clear, however, whether these results are due to enhanced perceptual processing or to a bias favoring the identification of emotionally significant stimuli over neutral stimuli. The present study used a two-alternative forced-choice perceptual identification task to disentangle the effects of bias and enhanced processing. We found that emotionally significant targets were better identified than neutral targets. In contrast, the emotional significance of the foil alternative had no effect on performance. The present results support the hypothesis that perceptual encoding of emotionally significant stimuli is enhanced.

Expertise in recognizing facial identity, and, in particular, sensitivity to subtle differences in the spacing among facial features, improves into adolescence. To assess the influence of experience, we tested adults and 8-year-olds with faces differing only in the spacing of facial features. Stimuli were human adult, human 8-year-old, and monkey faces. We show that adults' expertise is shaped by experience: They were 9% more accurate in seeing differences in the spacing of features in upright human faces than in upright monkey faces. Eight-year-olds were 14% less accurate than adults for both human and monkey faces (Experiment 1), and their accuracy for human faces was not higher for children's faces than for adults' faces (Experiment 2). The results indicate that improvements in face recognition after age 8 are not related to experience with human faces and may be related to general improvements in memory or in perception (e.g., hyperacuity and spatial integration).

In three experiments, we examined the mere-measurement effect, wherein simply asking people about their intent to engage in a certain behavior increases the probability of their subsequently engaging in that behavior. The experiments demonstrate that manipulations that should affect the ease of mentally representing or simulating the behavior in question influence the extent of the mere-measurement phenomenon. Participants who were asked about their intention to engage in various behaviors were more likely to engage in those behaviors than participants not asked about their intentions in situations in which mentally simulating the behavior in the intention question was relatively easy. We tested this ease-of-representation hypothesis using both socially desirable and socially undesirable behaviors, and our dependent variables comprised both self-reports and actual behaviors. Our findings have implications for survey research in various social contexts, including assessments of risky behaviors by public health organizations.

During binocular rivalry, incompatible images presented dichoptically compete for perceptual dominance. It has long been debated whether binocular rivalry can be controlled by attention. Most studies have shown that voluntary control over binocular rivalry is limited. We sought to remove attention from binocular rivalry by presenting a concurrent task. Diverting attention slowed the rivalry alternation rate, and did so in proportion to the difficulty of the concurrent task. Even a very demanding distractor task, however, did not arrest rivalry alternations completely. Given that diverting attention was equivalent to lowering the contrast of the rival stimuli, the ability of attention to speed binocular rivalry is most likely due to an increase in the effective contrast of the stimuli through boosting the gain of the cortical response. This increase in effective contrast will ultimately lead to a perceptual switch, thereby limiting voluntary control. Thus, attention speeds rivalry alternations, but has no inherent control over the rivalry process.

Animal studies suggest that early visual deprivation can cause permanent functional blindness. However, few human data on this issue exist. Given enough time for recovery, can a person gain visual skills after several years of congenital blindness? In India, we recently had an unusual opportunity to work with an individual whose case history sheds light on this question. S.R.D. was born blind, and remained so until age 12. She then underwent surgery for the removal of dense congenital cataracts. We evaluated her performance on an extensive battery of visual tasks 20 years after surgery. We found that although S.R.D.'s acuity is compromised, she is proficient on mid- and high-level visual tasks. These results suggest that the human brain retains an impressive capacity for visual learning well into late childhood. They have implications for current conceptions of cortical plasticity and provide an argument for treating congenital blindness even in older children.

This study examined the age and content of earliest childhood memories of self and others. European American and Taiwanese participants (N= 111) retrieved their earliest memories in response to the cue words self, mother, family, friend, and surroundings. Memory for mother was from an earlier age than memory for self, and memories for mother, family, and friend were more socially oriented in content than memories for self or surroundings. In addition, in response to all cue words, Euro-Americans recalled memories from an earlier age than did Taiwanese. Euro-Americans also had a greater tendency to report memories of specific events and focused more on their own roles and autonomy than did Taiwanese, who more often described routine events and emphasized the roles of others. These findings have important implications for infantile amnesia and the memory-self interplay.

We examined the effects of suggestion on Stroop interference in highly suggestible individuals. Participants completed the Stroop task with and without a suggestion to perceive Stroop words as meaningless symbols. Half the participants were given this suggestion in hypnosis, and half were given the suggestion without the induction of hypnosis. Suggestion produced a significant reduction in Stroop inhibition, accounting for about 45% of the variance in Stroop responding, regardless of whether hypnosis had been induced. These findings indicate that suggestion can at least partially overcome the automaticity associated with the Stroop effect.