Practice and probe items

Each task consisted of one practice item, followed by a block of 4-6 probe items as summarized in Table 3.2. General procedures for practice and probe items are outlined in Appendix B. Two consecutive probe items were used to probe each tense marker in the AUXILIARY DO, COPULA BE, and AUXILIARY BE categories. Auxiliary do, does, did and copula and auxiliary is, are, was, were were each probed in two sufficiently different contexts with different subject-tense marker combinations. Copula and auxiliary am only license one subject-tense marker combination (I am), which was probed twice. Five consecutive probe items probed -3s and –ed in sufficiently different contexts requiring inflection of different lexical verbs.

At least 5 items probed each category in sufficiently different contexts. A total of 5 items in one task probed tense markers in the -3s and –ed categories. A total of 6 items in one task probed tense markers in the AUXILIARY DO category. A total of 10 items across two consecutive tasks probed tense markers in the COPULA BE and AUXILIARY BE categories.

Each practice and probe item included visual stimuli (picture or video) and a verbal cue.

Use of manipulatives was minimized. Puppets were used to probe AUXILIARY DO and auxiliary was and were as they are routinely used in comparable elicitation tasks (Leonard et al., 2003; Rice & Wexler, 2001).

Each practice item provided input demonstrating correct use of a tense marker that would be probed in the upcoming task. Practice items established the communication modality and task for an upcoming set of probe items in a consequence-free environment with no penalty for incorrect responses. Practice items were presented in a similar format to probe items in the upcoming task. However, the author attempted to elicit a repetition of the correct response if a

production during presentation of the practice item. Repetition of the correct response was explicitly reinforced by praising the participant and repeating the participant’s utterance, “Good job! I like how you said _____.”

Probe items were structured in a way that required participants to spontaneously generate responses in the target modality. A flow chart for the presentation of probe items is shown in Figure 3.3. The author presented the visual stimuli and verbal cue corresponding to an item and gave a 10 second expectant delay waiting for the participant to spontaneously generate a response. Additional wait time was given if a participant was clearly still formulating a response. The cue and wait time were repeated once if the participant did not respond. If the participant generated a verbal response when the target communication modality was the graphic symbol modality, the child was prompted to “show me how you say that with the device.” This was followed by a 10 second expectant delay. If the participant generated a correct response, the response was reinforced with positive reinforcement as in the practice item. If the participant generated an incomplete or incorrect response or did not respond after the repeated cue, the cue was repeated and the correct response was produced in the target communication modality.

These items were scored as incorrect. For the AUXILIARY DO and auxiliary was/were tasks, pragmatically appropriate cues were given instead of a repetition of the initial verbal cue, as discussed in the section on stimulability tasks. Participants were allowed to repeat the modeled production of the correct response if their repetition was self-initiated. Repetition of the correct response was reinforced with positive reinforcement.

Items for copula and auxiliary is, are, was, and were and auxiliary does, do, and did were designed so participants were required to spontaneously generate a correct response by

Figure 3.3. Presentation of stimulability probe item in spoken modality.

combining a subject noun phrase with a target tense marker in the correct modality. The subjects were singular animal characters (the bird, the moose), plural animal characters (the bears, the zebras), singular inanimate objects (the wagon, the house) and plural inanimate objects (the cars, the trucks). Test items were designed to minimize the use of subject pronouns (he, she, it, they) in participant responses because high-frequency pronoun-tense marker combinations may be stored in associative memory as a whole unit. For example, the probe items for all forms of COPULA BE and auxiliary is, am, and are used grammatical cloze procedures in which the article the was supplied as part of the examiner’s verbal cue to prime participants to respond using a noun phrase.

For any given tense marker, each probe item required the participant to produce the target tense marker in a different context. For example, the two probe items for for copula is probed copula is in the context of two different low-frequency subject noun phrases (the bird is, the moose is). After the participant’s response was scored on the first copula is probe item, the author modeled production of the target response (the bird is). The second probe item required the participant to spontaneously generate a different response (the moose is) with no immediate prior exposure to this exemplar in the target modality. This use of multiple exemplars for morpheme stimulability tasks differs from the elicited imitation procedures used to probe phoneme stimulability in established assessment protocols (e.g., Goldman & Fristoe, 2015).