Interference from degraded auditory stimuli: linear effects of changing-state in the irrelevant sequence.

Cognitive performance, particularly on a number of tasks involving short-term memory for order, is impaired by the mere presence of irrelevant background sound. The current study examines the features of the irrelevant sound that determine its disruptive potency. Previous research suggests that the amount of variability in an irrelevant stream is related to the degree of disruption of memory. The present experiments used a parametric approach to manipulate degree of change more precisely. Increasing levels of degradation, effected either by low-pass filtering (speech) or by digital manipulation (speech and nonspeech), monotonically decreased the degree of interference. The findings support the following propositions: (i) the degree of physical change within an auditory stream is the primary determinant of the degree of disruption; and, (ii) the effects of irrelevant speech and irrelevant nonspeech sounds are functionally similar.