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The phenomena of disfluency clusters have been examined in the speech of children who stutter (CWS) and children who do not stutter (CWNS). Little is known about disfluency clusters in the adult population. The purpose of this study was to examine the characteristics of disfluency clusters in adults who stutter (AWS). The participants were ten AWS ranging in age from 18 to 60 (mean age = 35), with a stuttering severity of 9 to 30% (mean = 19%). Each participant provided a conversational speech sample of at least 300 words. Analysis focused on disfluency type, utterance length, speaking rate, and perceptual measures. Findings indicated that utterances containing disfluency clusters were significantly longer than fluent utterances and the speaking rate of fluent utterances was found to be significantly faster than that of disfluent utterances. Collectively the results appear to support a linguistic interpretation of disfluency clusters. The clinical implications of the findings are discussed.

The evolution of radio loud quasars is found to be strongly dependent upon their galaxy cluster environment. Previous studies (Yee and Green 1987) have shown that bright quasars at z ∼ 0.6 are found in clusters as rich as Abell richness class 1, while high luminosity quasars at lower redshifts are found only in poorer environments. An observational study of the environments of 66 low luminosity quasars with 0.3 < z < 0.6 yields several objects in rich clusters of galaxies. This result implies that radio loud quasars in these environments have faded approximately 3 magnitudes in the interval between redshifts 0.6 and 0.4, corresponding to a luminosity e-folding fading time of 900 million years, similar to the dynamical timescale of these environments. The analysis of low luminosity radio quiet quasars indicate that they are never found in rich environments, suggesting that they are a physically different class of objects. Properties of the quasar environment are investigated to determine constraints on the physical mechanisms of quasar formation and evolution. The optical cluster morphology indicates that the cluster cores have smaller radii and higher galaxy densities than are typical for low redshift clusters of similar richness. Radio morphologies may indicate that the formation of a dense intra-cluster medium is associated with the quasars' fading at these epochs. Galaxy colors appear to be normal, but there may be a tendency for clusters associated with high luminosity quasars to contain a higher fraction of gas-rich galaxies than those associated with low luminosity quasars, a result consistent with the formation of an ICM. Multislit spectroscopic observations of galaxies associated with high luminosity quasars indicate that quasars are preferentially located in regions of low relative velocity dispersion, either in rich clusters of abnormally low velocity dispersion, or in poor groups which are dynamically normal. This suggests that galaxy-galaxy interactions may play a role in quasar formation and sustenance. Virialization of rich clusters and the subsequent increase in galaxy velocities may therefore be responsible for the fading of quasars in rich environments.

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