Knight David C, Nguyen Hanh T, Bandettini Peter A
Laboratory of Brain and Cognition, National Institute of Mental Health, National Institutes of Health, Bethesda, MD 20892, USA.
Proc Natl Acad Sci U S A. 2003 Dec 9;100(25):15280-3. doi: 10.1073/pnas.2535780100. Epub 2003 Dec 1.
Conditional responding during simple Pavlovian conditioning is often characterized as a form of implicit memory. The extent to which this type of associative learning is independent of awareness is an issue of continuing debate. Previous studies have demonstrated conditioning in the absence of awareness. However, their results have been questioned based on methodological concerns with postexperimental questionnaires. In the present study, skin conductance response (SCR) and unconditioned stimulus (UCS) expectancy were measured concurrently as participants were exposed to a differential delay fear conditioning procedure in which one tone (CS+) predicted a loud white noise, whereas a second tone (CS-) was presented alone. UCS predictability was varied on a trial-by-trial basis by presenting conditioned stimuli (CSs) at volumes just above or below the perceptual threshold. Differential UCS expectancy (awareness) was observed only on perceived trials, whereas differential SCR developed on both perceived and unperceived trials. Although perceived stimuli elicited larger SCRs, the magnitude of conditioning, indexed by differential conditioned response expression (conditioned SCR to CS+ minus the SCR to CS-), was not influenced by stimulus perception. These data indicate that conditional fear can be expressed when individuals are unaware of fear-eliciting stimuli and suggest that the degree of conditioning is independent of awareness during differential Pavlovian fear conditioning.
在简单的巴甫洛夫条件反射过程中的条件反应通常被认为是一种内隐记忆形式。这种类型的联想学习在多大程度上独立于意识，是一个持续争论的问题。先前的研究已经证明在没有意识的情况下也能形成条件反射。然而，基于对实验后问卷的方法学担忧，他们的结果受到了质疑。在本研究中，当参与者接受差异延迟恐惧条件反射程序时，同时测量皮肤电反应（SCR）和无条件刺激（UCS）预期。在该程序中，一种音调（CS+）预示着一声响亮的白噪声，而另一种音调（CS-）单独呈现。通过在略高于或低于感知阈值的音量下呈现条件刺激（CSs），逐次试验地改变UCS的可预测性。仅在被感知的试验中观察到差异UCS预期（意识），而在被感知和未被感知的试验中均出现了差异SCR。尽管被感知的刺激引发了更大的SCR，但由差异条件反应表达（对CS+的条件SCR减去对CS-的SCR）所索引的条件反射程度不受刺激感知的影响。这些数据表明，当个体未意识到引发恐惧的刺激时，条件性恐惧仍可表现出来，并表明在差异巴甫洛夫恐惧条件反射过程中，条件反射的程度独立于意识。
