Task Demands Differentially Affect Processing of Intrinsic and Extrinsic Object Features in Working Memory.

Some argue that visual working memory operates on integrated object representations. Here, we contend that obligatory feature integration occurs with intrinsic but not extrinsic object features. Working memory for shapes and colors was assessed using a change-detection task with a central test probe, while recording event-related potentials (ERPs). Color was either an intrinsic surface feature of a shape or connected to the shape via a proximal but spatially disjunct extrinsic frame. There were two types of test: The direct test required memory for shape and color; the indirect test required only shape memory. Study-test changes of color were therefore either task-relevant or task-irrelevant. We assessed performance costs and event-related potential (ERP) effects arising from color changes. In the direct test, performance was poorer for extrinsic than intrinsic stimuli; task-relevant color changes elicited enhanced frontal negativity (N2, FN400) for both intrinsic and extrinsic stimuli. In the indirect test, performance costs and ERP effects associated with irrelevant color change were larger for intrinsic than extrinsic stimuli. This suggests intrinsic information is more readily integrated into the working-memory representation and evaluated against the test probe. Findings imply that feature integration is not obligatory under all conditions but influenced by stimulus-driven and task-related focus of attention.

Age-related changes in working memory: Age affects relational but not conjunctive feature binding.

In contrast to long-term memory, age-related association deficits in working memory are found only inconsistently. The authors hypothesized that type of binding is critical for the occurrence of such deficits. Relational binding abilities (associating separate visual units) should degrade with age, whereas more automatic conjunctive binding abilities (associating features within an object) should not. They contrasted associative memory and item memory using a change-detection task with colors and shapes in younger (18-33 years) and older (64-82 years) healthy adults. Color was either a surface feature of the shape (conjunctive binding) or a feature of a shape-external frame (relational binding). In a direct test of associative memory, participants memorized color-shape associations; in an indirect item memory test, participants were required to memorize only the shapes, and the authors measured the costs of ignoring task-irrelevant color changes from study to test. In the direct test, associative memory was poorer when relational binding was required rather than conjunctive binding, and associative memory was poorer in the older group, but no age-related association deficit was apparent. In the indirect test, by contrast, type of binding interacted with age: younger participants showed study-test congruence effects independent of the type of binding, but older adults showed enhanced congruence effects for conjunctive stimuli, indicating intact or even enhanced conjunctive binding, and practically no costs for relational stimuli, indicating poor relational binding. This stimulus-specific effect of a task-irrelevant feature change indicates that relational and conjunctive binding in working memory are differently affected by healthy aging. (PsycINFO Database Record