The Isolation Effect in Free Recall and Recognition

Abstract

Since 1933, when von Restorff first reported systematic research on the isolation effect, a continuous flow of publications has been devoted to this phenomenon (for a review, see Wallace, 1965). A central and yet unresolved problem in the interpretation of the effect is its locus in the sequence learning/retention/retrieval. Originally, von Restorff suggested processes like 'Bereichsbildung' on the trace level. Later, processes taking place during initial learning were emphasized; for example, Green (1956) thought the effect to be due to the pronounced 'surprise value' of the isolated item. More recently, attempts have been made to assess the importance of retrieval processes in the better retention of the isolated item. One way of doing this is to compare the strength of the isolation effect in recall versus recognition, as retrieval processes are generally more important in the former than in the latter. If the effect is largely due to input processes going on during initial learning, then the effect should be obtained in tests of both recall and recognition. If, however, the effect is mostly determined by retrieval processes, then one would expect the effect to be smaller or absent in tests of recognition. Surprisingly, only very few studies on the isolation effect have used tests of recognition. Most relevant to our purpose is a study by McLaughlin (1968). Using a serial anticipation task, he found a 'vivid' (isolated) item to be better retained than control items in tests of free recall if learning consisted of two or three trials; however, no such effect was found in tests of recognition that substituted for or followed the tests of recall. McLaughlin used CVCs, presented on slides, as learning material; vividness was produced by changing size (4 in. instead of 1.5 in.) and shape (uppercase bold instead of lowercase 'pica') of the letters. In