Relevance. The study of human functional states within the structural-functional approach is an important development in work psychology. As work becomes more intensive and cognitive, the study of mental fatigue becomes more important.

Objective. To validate cognitive tests for the assessment of mental fatigue cognitive effects, and to replicate cognitive effects of fatigue observed within the structural-functional approach.

Methodology. 27 subjects (18 male), engineers in a high-tech engineering firm, and took part in the study conducted over a working day in the morning and in the evening. Mental fatigue was assessed with a questionnaire. The cognitive tests included a test of attention switching, a test for working memory, and the Sternberg’s short-term memory search task.

Results. A reduction in attention switching and memory search efficiency was found. These results in a good concordance with previous results and indicate a reduction in the availability of top-down cognitive control resources. Evidence was found for transition towards sequential self-terminating memory search strategy under mental fatigue. No reduced working memory was found, which may be related to the meta-cognitive regulation of functional states.

Conclusions. Mental fatigue is associated with a reduction in the control of attention and short-term memory, related to the depletion of cognitive control resources. Individual cognitive reactions to fatigue are important. Future developments of the structural-functional approach may include the development of new diagnostics tools, the usage of cognitive modeling, the orientation to the analysis of the individual differences, and the integration of the structural-functional approach with resource approaches to cognition.