Sleep Deprivation Is a Common Situation Expe- Rienced by Individuals in Many Professions, including Those Who Perform Critical Roles

1 SLEEP DEPRIVATION IS A COMMON SITUATION EXPERIENCED BY INDIVIDUALS IN MANY PROFESSIONS, INCLUDING THOSE WHO PERFORM CRITICAL ROLES in society. These people include medical doctors, firefighters, parents, and members of the military.1-4 One of the most important and ubiquitous tasks faced by individuals in these important roles is that of categorization. Quick and accurate categorization is fundamental to survival and is critical in many professions for which sleep deprivation is common. For example, accurately categorizing an individual with chest pain as suffering from a heart attack could save the individual’s life, whereas categorizing the person as suffering from indigestion could lead to death. Similarly, for a soldier, accurately categorizing an individual as an enemy combatant or a civilian can be crucial for survival. Category learning involves laying down a memory trace that improves the efficiency of responding. It is now widely accepted that mammals have multiple memory systems, each of which is associated with different neural circuits.5-7 The predominant view is that different memory systems are better suited for learning different types of category structures.8-10 Two category learning domains that are of particular interest are rule-based and information-integration categories.8,11,12 Rule-based categories are those for which the optimal decision rule is cannot be verbalized. For example, if all members of 1 category are large, and all members of the other category are small, then the optimal strategy would be to determine the size of the target stimulus and to apply the following verbal rule: “If the stimulus is small place, it in category A; if the stimulus is large, place it in category B.” One of the most well-known and highly studied rule-based category learning tasks is the Wisconsin Card Sorting Task.13 Unlike rule-based categories, the optimal decision rule for information-integration categories is that it cannot be verbalized but, instead, requires a predecisional integration of information from 2 or more stimulus dimensions (usually expressed in different physical units). An example of information-integration categories composed of circular sine-wave gratings is shown in Figure 1. The optimal strategy (denoted by the solid diagonal line) cannot be verbalized because it involves a linear integration of information from dimensions expressed in incommensurable units (ie, orientation and spatial frequency). Optimal rule-based category learning is thought to be mediated by a hypothesis-testing system.8,10-12,14,15 The hypothesistesting system reasons in an explicit fashion and is dependent on conscious awareness. Optimal information-integration category learning is thought to be mediated by a procedural system.8,10-12,14,15 Unlike the hypothesis-testing system, the procedural learning system is not consciously penetrable and, instead, operates by Sleep Deprivation anD information integration