What scientific concept concerning skill generalization was often viewed skeptically by researchers regarding early cognitive training protocols?

Transfer effects

Transfer effects represented a crucial scientific hurdle in the early research phase of cognitive training. Researchers were intensely interested in determining whether practicing a very specific mental skill in a controlled laboratory setting—such as improving reaction time on a specific screen prompt—would yield measurable, lasting improvements in unrelated, everyday tasks. For many years, the prevailing scientific consensus leaned toward skepticism, suggesting that improvements often remained strictly limited to the specific task that was practiced during the drills. This limitation created a significant gap between the rigorous, targeted results achievable in the lab and the broad, generalized claims the commercial market would later attempt to market to consumers.