The role of attention in retaining the binding of integral features in working memory

Previous studies have suggested that retaining bindings in working memory (WM) requires more object-based attention than retaining constituent features. However, we still need to address the object-based attention hypothesis to determine both the generality (Does the object-based attention hypothesis of binding apply to feature bindings other than those tested?) and the reality (Was the observed effect in previous studies an artifact of the testing process?). We addressed these two issues by focusing on the binding of integral features, which was ignored in previous studies. Integral features can be manipulated independently but cannot be attended to or processed independently of each other, and they are primarily perceived in a more unitary fashion. Consequently, integral-feature bindings should be processed as integrated units without the help of extra object-based attention. We examined whether or not the object-based attention hypothesis applied to integral-feature bindings (generality), and these results enabled us to check the reality of the hypothesis. In line with our prediction, we found that a secondary task consuming object-based attention did not selectively impair the binding performance (Experiments 1, 2, 3, 5, and 7). The absence of selective binding impairment was not attributable to the use of an invalid secondary task (Experiment 4), failure to memorize the binding between length and width (Experiment 6), tapping the incorrect type of attention (Experiment 6), the feasibility of feature categorization (Experiment 7), or poor task performance (Experiment 7). Overall, these results suggest that the object-based attention hypothesis does not fit for the integral-feature bindings, and that the pivotal role of object-based attention reported by previous studies was reliable.