The auditory/verbal short-term memory of 64 college students was examined across a wide range of retention intervals (5 seconds to 60 seconds). High attention during interpolated processing was ensured by monitoring rehearsal with a combination of methods, and errors were analyzed for evidence of proactive and intra-unit interference. Recall of three- and five-digit items was excellent under the conditions of modality isolation of interpolated processing. In fact, only 4% of all three-digit items and 10% of all five-digit items were forgotten for reasons other than proactive intrusion of intra-unit interference. The results support an interdependent model of attention and modality effects in short-term forgetting. (Author/FL)