The Effect of Midazolam on Visual Search: Implications for Understanding Amnesia

The notion of multiple memory systems based on conscious accessibility has been supported largely by neuropsychological patient studies. Specifically, it was widely held that amnesic patients have impaired explicit memory performance but spared implicit memory performance. However, recent patient studies have called the implicit/explicit memory distinction into question. In this study, normal participants were tested on a visual search task, once after an injection of midazolam, an anesthetic that induces temporary amnesia, and once after an injection of saline. Under the influence of midazolam, participants did not show facilitation in search times for repeated configurations (contextual cuing), although there was a general speed-up in performance across blocks in both the midazolam and saline conditions. Neither the contextual-cuing effect nor the procedural-learning effect was available to subjective experience, yet only one of these was affected by midazolam-induced amnesia. These data call into question the notion that memory systems divide on the basis of subjective experience of consciousness or reportability. Rather, the findings support the contention that anterograde amnesia affects learning that depends on building novel associations in memory and that this deficit does not hinge upon accessibility to consciousness.