Summary knowledge of results for skill acquisition: support for the guidance hypothesis.

Summary knowledge of results (KR) involves the presentation KR for each of a set of trials (e.g., 10) only after the last trial in the set has been completed. Earlier, Lavery (1962) showed that, relative to providing KR after each trial, a 20-trial summary KR was detrimental to performance in a practice phase with KR present but was beneficial for a no-KR retention test. Using a relatively simple ballistic-timing task, we examined summary lengths of 1 (essentially KR after every trial), 5, 10, and 15 trials, searching for an inverted-U relationship between summary length and retention performance as predicated by a guidance hypothesis for KR. During acquisition when KR was present and being manipulated, all groups showed improvements in performance across practice, while increased summary lengths generally depressed performance. However, in a delayed no-KR retention test, there was an inverse relation between the summary length in acquisition and absolute constant error on the retention test. A guidance hypothesis is favored to explain how, relative to immediate KR, long KR summaries can provide detrimental effects in acquisition while enhancing retention performance.