Date on Master's Thesis/Doctoral Dissertation


Document Type

Doctoral Dissertation

Degree Name

Ph. D.


Psychological and Brain Sciences

Committee Chair

Zahorik, Pavel

Author's Keywords

Irrelevant speech effect; Short-term memory; Development


Short-term memory; Memory--Effect of sound on; Memory--Effect of noise on; Speech


The Irrelevant Speech Effect (ISE) is a phenomenon in which the presentation of auditory materials (typically speech) impairs the serial recall of visually presented materials, either digits or letters. Although this effect has been replicated in a large number of studies, a wide range of individual differences in susceptibility to the auditory distracters has been found. The current study investigates four possible determinants of individual differences of the ISE: (1) The sequence length of the short-term memory (STM) task, (2) the content of the STM task and auditory distracter, (3) the STM capacity of the individual, and (4) developmental differences. Results from a series of experiments suggest that (1) increasing sequence length can have substantial negative effects on STM task performance, but it does not increase the ISE. This indicates that individual differences in the ISE do not depend on individual differences related to task difficulty. (2) When sequence length is adjusted to equate STM task performance, the ISE is only observed for speech distracters. This result is important because it implies a primary role of phonological rehearsal in the ISE. Additional testing with a vi suo-spatial STM task that did not require rehearsal showed a release from the ISE. (3) Individuals with high memory capacity appear to be less susceptible to the ISE. This result is among the first to demonstrate the roll of STM capacity in the ISE, and is consistent with past work that shows relationships between working memory capacity (WMC) and susceptibility to distraction. (4) When tested at span (the longest sequence length an individual can recall 50% of the time), children and adults show similar magnitudes of the ISE. This too is consistent with the view that the ISE is related to memory capacity, rather than age. Taken together, these outcomes indicate that the ISE is caused by a disruption of memory encoding at the phonological rehearsal stage, which in tum is related to memory capacity. These results inform theory development of STM and the processes involved in auditory attention. In addition, results may be applied to the improvement of acoustical conditions in learning environments.