Single subject controlled experiments in aphasia: the science and the state of the science

Abstract

This paper discusses the use of single subject controlled experimental designs for investigating the effects of treatment for aphasia. A brief historical perspective is presented, followed by discussions of the advantages and disadvantages of single subject and group approaches, the basic requirements of single subject experimental research, and crucial considerations in design selection. In the final sections, results of reviews of published single subject controlled experiments are discussed, with emphasis on internal validity issues, the number of participants enrolled in published studies, operational specification of the dependent and independent variables, and reliability of measurement.

Learning outcomes: As a result of reading this paper, the participant will: (1) understand the mechanisms required for demonstration of internal and external validity using single subject controlled experimental designs, (2) become familiar with the basic requirements of single subject controlled experimental research, (3) understand the types of single subject controlled experimental designs that are the most appropriate for studying the effects of treatment for aphasia, and (4) become familiar with trends in the published aphasia treatment literature in which single subject controlled experimental designs have been used.

Figures

Fig. 1

ABA design strategy used by Renvall et al. (in press) to examine the effects of contextual priming on naming in a patient with anomia. Naming performance on trained and control items during A phases of the study and that on trained items during the B (treatment) phase is shown. Reprinted with permission.

Fig. 2

Multiple baseline design used by Kiran and Thompson (2003) to investigate the effects of semantic complexity in treatment of naming in fluent aphasic participants. Naming performance on typical, intermediate, and atypical items for the category birds and that on atypical, intermediate, and typical items for the category vegetables is shown for Participant 1 in the study. Reprinted with permission.

Fig. 3

Alternating treatment design, combined with a multiple baseline design across behaviors, used by Wambaugh (2003) to examine the effects of phonologic cueing (PCT) vs. semantic cueing treatment (SCT) in a single patient with chronic anomia. Percentage correct naming of word sets is shown across phases of the study. Reprinted with permission.

Fig. 4

Aphasia treatment studies by design type published from 2000 to 2005.

Fig. 5

Aphasia treatment studies published by journal from 2000 to 2005.

Fig. 6

Published single subject controlled experimental studies demonstrating internal validity in 1978–1987, 1988–1999, and 2000–2005 reviews of the literature.

Fig. 7

Number of participants in published single subject controlled experiments in 1978–1987, 1988–1999, and 2000–2005 reviews of the literature.

Fig. 8

Published single subject controlled experiments reporting reliability data in 1978–1987, 1988–1999, and 2000–2005 reviews of the literature.