The purpose of this study is to determine the optimal treatment intensity of a word learning intervention for improved measures of vocabulary immediately post intervention and at 6-months follow up by addressing 3 specific aims.
1. to determine whether low frequency (massed) or high frequency (distributed) conditions are more effective intervention schedules with respect to children's vocabulary gains during treatment. Using a causally interpretable research design with children randomly assigned to both conditions, the investigators will test the hypothesis that high frequency treatment will be more effective than low frequency schedules, informed from our own research as well as that proposed by distributed learning theorists. The investigators propose that the greatest gains will be observed immediately post intervention as well as 6-months post intervention for children who receive high-frequency treatment as compared to children who receive low-frequency treatment.
2. to determine the optimal number of dose exposures within each condition of frequency. Using a causally interpretable research design, with planned variations in dose, the investigators will test the hypothesis that increases in dose are beneficial when treatment frequency is low, and similarly that low levels of dose are beneficial when frequency is high. The investigators propose that the greatest gains will be observed for children who receive high-frequency/low-dose or low-frequency/high-dose treatments as compared to children who receive high-frequency/high-dose or low-frequency/low-dose treatments.
3. to identify thresholds of cumulative intensity after which additional exposures provide no additional benefit to children's vocabulary gains, corresponding to a point of 'diminishing returns'. The investigators will test the hypothesis that for both low-frequency and high-frequency treatments, there is a point at which increases in treatment dose do not correspond to any additional gains in children's vocabulary skills during treatment.
The proposed study features a two-group pre/post experimental design with random assignment to target words across six dose exposures. Using blocked random assignment, each child will first be randomized to a low-or high-frequency treatment condition. Target words will then be randomly assigned to one of six dose exposures (0, 4, 8, 12, 16, 20 with 0 serving as a control). Thus, this study will measure both between child (frequency) and within child (dose) variance attributed to intensity of treatment. Children who meet all eligibility criteria and are enrolled in the study will be randomly assigned to one of the two conditions, high-or low-frequency, as previously described.
Each child will receive one-on-one treatment sessions each week for 10 weeks according to their assigned frequency (one or four sessions per week for a total of 10 or 40 sessions, respectively) over the summer period. Each session will follow an efficacious word learning intervention. The word learning intervention uses the 10 commercially available children's books from previous studies. Each week, 2 of the 10 storybooks will be read, with 3 of the 6 vocabulary words targeted from each book. The book and words targeted will be consistent between frequency conditions. For the high-frequency condition, each book will be read once per session across 4 sessions, for a total of 4 readings per book each week. For the low-frequency condition, each book will be read 4 times in 1 session for a total of 4 readings per book each week, thereby keeping the number of book-readings equal across conditions. Over the course of the 10-week intervention, two books will be read each week and all 10 books will be read twice throughout the intervention. Three of the 6 targeted words will be taught the first week the book is read and the other 3 of 6 targeted words taught the second week the book is read. Each child will receive a total of 120 minutes of therapy each week, which equates to 14-16 hours of therapy (approximately 4 hours of therapy per day for 4 days).
The word learning intervention is designed to increase children's word learning abilities using rich, robust word learning strategies within story book readings including provision of a synonym (e.g., A furnace is like a heater), definition (e.g., Furnace means something used to make heat to warm buildings), and context sentence (e.g., Today it was cold outside so mom turned on the furnace) during pre-book reading, book reading, and post-book reading activities. During the pre-book reading, the intern will discuss the target words that the child will hear in the book, with the exception of the word assigned to the 0 exposure condition. During this portion of the intervention, the speech-language intern will use zero, one or two strategies, depending on the assigned dose. During the book reading portion of the intervention, the intern will read the book in its entirety. The intern will either not elaborate the target word (0 dose) or will offer a synonym as the word is read in the book. During the post-book reading, the intern will use zero, one, or two strategies depending on the assigned dose.
