Selective storage and maintenance of an object's features in visual working memory

Woodman, G. F., & Vogel, E. K. (2008). Selective storage and maintenance of an object's features in visual working memory. Psychonomic Bulletin & Review, 15, 223-229.

Abstract:
It has been shown that we have a highly capacity-limited representational space with which to store objects in visual working memory. However, most objects are composed of multiple feature attributes, and it is unknown whether observers can voluntarily store a single attribute of an object without necessarily storing all of its remaining features. In this study, we used a masking paradigm to measure the efficiency of encoding, and neurophysiological recordings to directly measure visual working memory maintenance while subjects viewed multifeature objects and were required to remember only a single feature or all of the features of the objects. We found that measures of both encoding and maintenance varied systematically as a function of which object features were task relevant. These experiments show that individuals can control which features of an object are selectively stored in working memory.

Note:
This paper discussed the obligatory storage hypothesis and the selective feature storage hypothesis (flexible encoding hypothesis). The former one suggests that when an object is attended, all features are encoded. In contrast, the latter hypothesis, a task-relevant feature can be selectively processed without processing the task-irrelevant feature.

A change detection task is performed.
They measured the capacity coefficient (k) as a function of the SOA between memory array and mask to compute the consolidation rate. Color, orientation (shape), or conjunction features were instructed to attend. Results showed the consolidation rate (slope of that function) of color is higher than orientation (shape) and conjunction. It is suggests that feature selection may alter the encoding of stimuli.
To test the selective storage, they conducted an ERP experiment by testing the CDA component which is observed at the posterior parietal site. The amplitude of CDA may show different features is retained in memory. Given the same stimulus array, amplitude of CDA is higher when attending to color. In contrast to the obligatory encoding hypothesis (it may predict the equal amplitude), it supports the selective feature encoding hypothesis.


My comment:
*The method section is not clear enough, I wonder if the capacity function varied as a function of task-relevancy. From my understanding, the authors just pooled all the types of changes (relevant/ irrelevant) as a single condition.
*Because color is salient, it can be processed wile ignoring the orientation (shape) feature)