Breadth–Depth Interaction in ESP Vocabulary among Moroccan Mid-Professional Tourist Agents: Instructional Focus and Insights from the Dual-Route Cascaded Framework

Abstract

This study investigates the breadth–depth interaction in English for Specific Purposes (ESP) vocabulary among Moroccan mid-professional tourist agents (MPTAs). A long-standing debate in vocabulary research concerns whether vocabulary breadth and depth represent distinct dimensions or different manifestations of a single underlying construct. To explore this issue, two instructional experiments were conducted in Marrakech (N = 10) and Agadir (N = 18). Results from the breadth-oriented experiment in Marrakech revealed a high vocabulary uptake rate of 6.67 words per contact hour, significantly exceeding the established benchmarks of 3.8 to 5.4 words per hour (Milton, 2009). However, despite these gains, statistical analysis yielded a weak correlation (r = 0.29) and high variance (SD = 27.66), suggesting uneven development across lexical dimensions. This pattern may be consistent with reliance on the direct lexical route proposed by the Dual-Route Cascaded (DRC) model (Coltheart et al., 2001), whereby rapid form–meaning mappings develop without corresponding growth in qualitative word knowledge. In contrast, the depth-oriented instruction in Agadir produced a very strong correlation (r = 0.94), indicating a substantially stronger relationship between vocabulary breadth and depth. This pattern may reflect a greater degree of statistical stability and more integrated lexical development, although further research is required to verify the cognitive mechanisms involved. Overall, the findings suggest that the breadth–depth relationship may be sensitive to instructional emphasis. Nevertheless, given the relatively small sample sizes, participant attrition across post-tests, and the wide confidence interval observed in the breadth-oriented condition, the findings should be interpreted cautiously and regarded as exploratory rather than conclusive. The study contributes to ongoing discussions concerning the dimensionality of vocabulary knowledge and highlights the potential role of instructional focus in shaping lexical development among learners in specialized ESP contexts.