Bowers Robert Ian, Timberlake William
Cognitive Science, Indiana University, Bloomington, IN, USA; School of Psychology, Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal.
Psychological and Brain Sciences , Indiana University , Bloomington, IN , USA.
R Soc Open Sci. 2017 Feb 8;4(2):160994. doi: 10.1098/rsos.160994. eCollection 2017 Feb.
If acquired associations are to accurately represent real relevance relations, there is motivation for the hypothesis that learning will, in some circumstances, be more appropriately modelled, not as direct dependence, but as conditional independence. In a serial compound conditioning experiment, two groups of rats were presented with a conditioned stimulus (CS1) that imperfectly (50%) predicted food, and was itself imperfectly predicted by a CS2. Groups differed in the proportion of CS2 presentations that were ultimately followed by food (25% versus 75%). Thus, the information presented regarding the relevance of CS2 to food was ambiguous between direct dependence and conditional independence (given CS1). If rats learnt that food was conditionally independent of CS2, given CS1, subjects of both groups should thereafter respond similarly to CS2 alone. Contrary to the conditionality hypothesis, subjects attended to the direct food predictability of CS2, suggesting that rats treat even distal stimuli in a CS sequence as immediately relevant to food, not conditional on an intermediate stimulus. These results urge caution in representing indirect associations as conditional associations, accentuate the theoretical weight of the Markov condition in graphical models, and challenge theories to articulate the conditions under which animals are expected to learn conditional associations, if ever.
如果习得的关联要准确代表真实的相关性关系，那么就有理由提出这样的假设：在某些情况下，学习更适合被建模为条件独立，而非直接依赖。在一个系列复合条件作用实验中，两组大鼠被给予一个条件刺激（CS1），它对食物的预测并不完美（50%），且自身又被CS2不完美地预测。两组的区别在于最终跟随着食物的CS2呈现比例（25%对75%）。因此，关于CS2与食物相关性所呈现的信息在直接依赖和条件独立（给定CS1）之间是模糊的。如果大鼠了解到给定CS1时食物与CS2是条件独立的，那么两组的实验对象此后对单独的CS2应该有相似的反应。与条件性假设相反，实验对象关注的是CS2对食物的直接可预测性，这表明大鼠将CS序列中的远端刺激也视为与食物直接相关，而非依赖于中间刺激。这些结果促使在将间接关联表示为条件关联时要谨慎，突出了图形模型中马尔可夫条件的理论重要性，并挑战理论去阐明动物在何种条件下（如果有的话）有望学习条件关联。
