Neuronal Activity in the Visual Cortex Reveals the Temporal Order of Cognitive Operations

Most mental processes consist of a number of processing steps that are executed sequentially. The timing of the individual mental operations can usually only be estimated indirectly, from the pattern of reaction times. In vision, however, many processing steps are associated with the modulation of neuronal activity in early visual areas. Here we exploited this association to elucidate the time course of neuronal activity related to each of the self-paced mental processing steps in complex visual tasks.We trained monkeys to perform two tasks, search-traceandtrace-search,whichrequired performing a sequence oftwooperations: a visual search for a specific colorandthemental tracing of a curve. We used multielectrode recording techniques to monitor the representations of multiple visual items in area V1 at the same timeandfoundthat the relevant curve as well as the target of visual searchevokedenhancedneuronal activity with a timing thatdependedonthe order of operations. This modulation of neuronal activity in early visual areas could allow these areas to (1) act as a cognitive blackboard that permits the exchange of information between successive processing steps of a sequential visual task and to (2) contribute to the orderly progression of task-dependent endogenous attention shifts that are driven by task structure and evolve over hundreds of milliseconds. Copyright © 2010 the authors