Measurement of intelligibility in disordered speech

To determine empirically which of three frequently observed rules in children with phonological disorders contributes most to difficulties in speaker intelligibility.

To evaluate the relative effects on intelligibility of deletion of final consonants (DFC), stopping of fricatives and affricates (SFA), and fronting of velars (FV), phonologically reduced sentences were read to groups of adult listeners at normal levels of occurrence for typical conversation and at equal levels of occurrence.

DFC had a greater effect than SFA on intelligibility, which had a greater effect than FV on intelligibility, when these rules occurred at levels approximating those seen in typical conversational speech. Results differed, however, when opportunities for rule occurrence were equalized. At relatively low levels of occurrence, FV had less effect on intelligibility than did SFA and DFC, but no significant differences in intelligibility were found between the latter two rules. At relatively high levels of occurrence, no significant differences between the three rules were observed.

These findings may be important clinically for clinicians who are trying to determine which rules should be targeted first in therapy.