Bedform segregation and locking increase storage of natural and synthetic particles in rivers.

While the ecological significance of hyporheic exchange and fine particle transport in rivers is well established, these processes are generally considered irrelevant to riverbed morphodynamics. We show that coupling between hyporheic exchange, suspended sediment deposition, and sand bedform motion strongly modulates morphodynamics and sorts bed sediments. Hyporheic exchange focuses fine-particle deposition within and below mobile bedforms, which suppresses bed mobility. However, deposited fines are also remobilized by bedform motion, providing a mechanism for segregating coarse and fine particles in the bed. Surprisingly, two distinct end states emerge from the competing interplay of bed stabilization and remobilization: a locked state in which fine particle deposition completely stabilizes the bed, and a dynamic equilibrium in which frequent remobilization sorts the bed and restores mobility. These findings demonstrate the significance of hyporheic exchange to riverbed morphodynamics and clarify how dynamic interactions between coarse and fine particles produce sedimentary patterns commonly found in rivers.

Cryptosporidium oocyst persistence in agricultural streams -a mobile-immobile model framework assessment.

Rivers are a means of rapid and long-distance transmission of pathogenic microorganisms from upstream terrestrial sources. Pathogens enter streams and rivers via overland flow, shallow groundwater discharge, and direct inputs. Of concern is the protozoal parasite, Cryptosporidium, which can remain infective for weeks to months under cool and moist conditions, with the infectious stage (oocysts) largely resistant to chlorination. We applied a mobile-immobile model framework to assess Cryptosporidium transport and retention in streams, that also accounts for inactivation. The model is applied to California's Central Valley where Cryptosporidium exposure can be at higher risk due to agricultural and wildlife nonpoint sources. The results demonstrate that hyporheic exchange is an important process to include in models characterizing pathogen dynamics in streams, delaying downstream transmission and allowing for immobilization processes, such as reversible filtration in the sediments, to occur. Although in-stream concentrations decrease relatively quickly (within hours), pathogen accumulation of up to 66% of the inputs due to immobilization processes in the sediments and slower moving surface water could result in long retention times (months to years). The model appropriately estimates baseflow pathogen accumulation and can help predict the potential loads of resuspended pathogens in response to a storm event.

Retention and remobilization dynamics of fine particles and microorganisms in pastoral streams.

Both microbial metabolism and pathogen retention and remobilization are dependent on downstream transport of fine particles, which migrate in a series of deposition and resuspension events. All fine particles, including clay minerals, particulate organic carbon, nutrients and microbes, are often considered to be transported similarly in the environment because of a lack of specific observations comparing their relative transport. We conducted a tracer injection study to compare the transport and retention of the fecal indicator bacterium Escherichia coli, synthetic inert fluorescent fine particles, and a dissolved conservative tracer. We found that the fluorescent fine particles and bacteria were transported similarly, with both having greater retention than the solute tracer. We used a stochastic model to evaluate in-stream retention and migration of the solute, fluorescent particles, and E. coli. The best-fit model parameters indicate that different stream reaches had varied retention characteristics, but always showed greater retention of fluorescent particles and E. coli compared to the solute tracer. Direct measurements within known retention areas after the injection showed that the majority of the fluorescent particles and E. coli were retained near the sediment-water interface in macrophyte stands or filtered within the top 3 cm of the streambed sediment. Both the tracer particles and E. coli were retained within these regions for multiple months following the injection experiment. The stochastic model properly captured the wide range of storage timescales and processes we observed in the stream. Our results demonstrate the importance of the streambed sediment and in-stream macrophytes as short- and long-term reservoirs for fine organic particles and microbes in streams.

An operant intervention for early stuttering. The development of the Lidcombe program.

Stuttering is a common speech disorder that causes significant distress and may cause social maladjustment and hinder occupational potential. Treatments for chronic stuttering in adults can control stuttering by teaching the speaker to use a new speech pattern. However, these treatments are resource intensive and relapse prone, and they produce speech that sounds unnatural to the listener and feels unnatural to the speaker. This article describes the development and evaluation of an operant treatment for early stuttering. Parents are trained to present verbal contingencies for stuttered and stutter-free speech during everyday speaking situations with their children. The authors overview outcome data from several studies that suggest that this program produces relapse-free control of stuttered speech in preschool children in the medium and long term in a cost-effective manner.

Novel speech patterns and the treatment of stuttering.

Variants of rhythmic speech and legato speech have been used for centuries to treat stuttering. Despite considerable empirical and theoretical inquiry, the reason for the effectiveness of these novel speech patterns in suppressing stuttering is unknown. Recent acoustic research conducted at the University of Sydney suggests that a reduction in the variability of syllabic stress is a critical feature of these two speech patterns, and that this reduction suppresses stuttering by stabilizing the speech motor system. This paper reviews what is known about rhythmic speech and legato speech from this perspective, and the theoretical and clinical implications of reconceptualizing them in this way are discussed.

Treating stuttering in young children: predicting treatment time in the Lidcombe Program.

It is known that children may recover from stuttering without formal treatment during the first years after onset. Consequently, the timing of professional, early stuttering intervention is a pressing issue in speech-language pathology. This report presents data pertinent to this issue for 261 preschool-age children who received the Lidcombe Program of early stuttering intervention. Of these children, 250 completed the program and were considered by their clinicians to have been treated successfully. For the children who were treated successfully, logistical regression analyses were used to determine whether age, gender, period from onset to treatment, and stuttering severity related systematically to the time required for treatment. The present data confirmed previous reports that a median of 11 clinic visits was required to achieve zero or near-zero stuttering with the Lidcombe Program. Results were also consistent with a preliminary report of 14 children (C. W. Starkweather & S. R. Gottwald, 1993) showing a significant relation between stuttering severity and the time needed for treatment, with children with more severe stuttering requiring longer treatment times than children with less severe stuttering. However, results did not associate either increasing age or increased onset-to-treatment intervals with longer treatment times. This finding is not consistent with the Starkweather and Gottwald report, which linked advancing age with longer treatment time. In fact, the present data suggest that, for a short period after stuttering onset in the preschool years, a short delay in treatment does not appear to increase treatment time. An important caveat to these data is that they cannot be generalized to late childhood or early adolescence. The present findings are discussed in relation to natural recovery from stuttering.

Control of children's stuttering with response-contingent time-out: behavioral, perceptual, and acoustic data.

Many stuttering treatments incorporate contingencies for stuttering that are thought to contribute to treatment effectiveness. One contingency used in a number of treatment programs for children is time-out (TO) from speaking. However, although TO has been shown to control stuttering in adults there are no clear demonstrations of this effect in children. One aim of the present study was to demonstrate in the laboratory that TO reduces stuttering in children. Three school-age children spoke in a single-subject ABA experiment. In the B phase, a red light was illuminated for 5 seconds when the subject stuttered, during which time the subject stopped talking. Two of the three children showed clear reductions in stuttering in response to TO. The second aim of the study was to detect whether the children who responded to To adopted an unusual speech pattern in order to control their stuttering. Listeners did not detect any differences between the perceptually stutter-free speech of baseline conditions and that of TO conditions, and a subsequent acoustic analysis revealed a reduction in the variability of vowel duration during TO in one subject and no changes in the other. The theoretical and clinical implications of the findings are discussed.

Speech outcomes of a prolonged-speech treatment for stuttering.

It has been shown that people who stutter can speak with greatly reduced stuttering after treatments that use variations of Goldiamond's (1965) prolonged-speech (PS). However, outcome research to date has not taken account of several important issues. In particular, speech outcome measures in that research have been insufficient to show that lasting relief from stuttering has been achieved by clients outside the clinic for meaningful periods. The present study used extensive speech outcome measures across a variety of situations in evaluating the outcome of an intensive PS treatment (Ingham, 1987). The speech of 12 clients in this treatment was assessed on three occasions prior to treatment and frequently-on eight occasions-after discharge from the residential setting. For 7 clients, a further assessment occurred at 3 years posttreatment. Concurrent dependent measures were percent syllables stuttered, syllables per minute, and speech naturalness. The dependent measures were collected in many speaking situations within and beyond the clinic. Dependent measures were based on speech samples of substantive duration, and covert assessments were included in the study. Detailed data were presented for individual subjects. Results showed that 12 subjects who remained with the entire 2-3-year program achieved zero or near-zero stuttering. The majority of subjects did not show a regression trend in %SS or speech naturalness scores during the posttreatment period, either within or beyond the clinic. Some subjects showed higher posttreatment %SS scores during covert assessment than during overt assessment. Results also showed that stuttering was eliminated without using unusually slow and unnatural speech patterns. This treatment program does not specify a target speech rate range, and many clients maintained stutter-free speech using speech rates that were higher than the range typically specified in intensive PS programs. A significant correlation was found between speech rate and perceived posttreatment speech naturalness.

Prolonged speech and modification of stuttering: perceptual, acoustic, and electroglottographic data.

Prolonged speech and its variants are a group of novel speech patterns that form the basis of a popular treatment for stuttering (Ingham, 1984). It is difficult to determine which features of prolonged speech are necessary for the elimination of stuttered speech because the speech pattern produces simultaneous changes in respiratory, laryngeal, and articulatory activity. Experimental studies have shown that the modification of phonation and of speech rate contributes to stuttering reduction, and increased duration of speech segments and reduced variability of vowel duration are known to occur as a result of prolonged-speech treatment programs. However, previous studies of prolonged speech have all instructed subjects to modify their customary speech patterns in a particular way. The aim of the present study was to investigate changes in the speech pattern of individual subjects when stuttering was modified with prolonged speech without specific instruction in how this should be done. In one experimental phase, 3 subjects showed clinically significant stuttering reductions when instructed to use whichever features of prolonged speech they needed to reduce their stuttering. The resulting perceptually stutter-free speech was judged to be natural sounding. Stuttering in a fourth subject reduced without experimental intervention. Recordings of acoustic and electroglottographic signals from the 4 subjects were analyzed. Changes in the variability of vowel duration occurred in all subjects. Theoretical and clinical implications of the results are discussed.

A further evaluation of the speech of stutterers during chorus- and nonchorus-reading conditions.

The claim that stutterers change their customary way of speaking during chorus-reading conditions was assessed in a single subject experimental design on the speech of three stutterers. A number of pairs of speech samples of identical prose were obtained from chorus- and nonchorus-reading conditions for each stutterer. Observers judged whether the pairs were composed of samples drawn from same (chorus/chorus or nonchorus/nonchorus) or different (chorus/nonchorus) oral reading conditions. The findings aligned with those obtained in an earlier group study. They indicated that there may be changes in the speech pattern of some stutterers during chorus-reading conditions, but this change may not occur in the speech pattern of all stutterers who respond to chorus reading conditions.

On-line measurement of aphasic speech.

Seven response categories, devised for the concurrent evaluation of aphasic speech, were investigated for their reliability. The spontaneous speech of 5 aphasic subjects was rated on-line by 4 clinicians using 7 response categories. Agreement among the 4 judges, for both inter-judge and intra-judge reliability, varied for each subject and was not high enough to support the concurrent use of the seven response categories for the on-line investigation of aphasic speech in all subjects. Ways in which the reliability of the categories might be increased are discussed.

Perceptual assessment of normalcy of speech following stuttering therapy.

Stuttering therapy procedures such as rhythmic or prolonged speech have been criticized because afterward the subject may speak fluently but also abnormally. Although assessments of the normalcy of speech behavior have been rare, some recent procedures have included perceptual assessments of certain dimensions of speech behavior. This study reports an evaluation procedure where listeners endeavored to distinguish between intermingled speech samples obtained from treated stutterers and a peer group of normally fluent speakers. Different groups of listeners were asked to judge the prosody, rate, fluency, and naturalness of posttreatment samples from a group of stutterers treated with a prolonged speech procedure, and a matched peer group of noramlly fluent speakers. No significant differences were found between the assessments of stutters and normally fluent speakers. However, when another group of listeners was asked to decide whether the speech samples were from treated stutters or normal speakers, the stutters received significantly fewer normal speaker judgements. Interrelationships between the judgment scales were evaluated along with a forced-choice procedure for assessing the normalcy of individual speech samples.

Treatment and generalization effects in an experimental treatment for a stutterer using contingency management and speech rate control.

An experimental treatment program for an adult stutterer, using contingency management and rate control procedures, is described. During laboratory sessions, a combination of both procedures resulted in maintained stutter-free speech within a target speech rate range. Bidaily recordings of the subject's speech across all nonlaboratory speaking situations, preceding and throughout the laboratory treatment, revealed no correspondence between laboratory and nonlaboratory speech behavior. Some positive and negative findings from this study are considered with respect to contingency management of stuttering.