Factor analysis and the cerebral hemispheres: “Unlocalized” functions

Previous factor analyses have employed lateralized task tapping processes (functions) whose localizations are thought to be known at the level of the cerebral lobe or finer. Here nine tasks are introduced to factor analysis whose underlying processes have unknown localization. A new function identified as auditory emotional is found to be independent of asymmetry in a visual emotion judgment task, suggesting that lateralized emotion judgments depend on modality specific processes. A second new function identified as visual temporal is found to be independent of asymmetries in visual language recognition, posing constraints on theories that link lateralized language processes to processes dealing with temporal sequencing. Another important finding is that the recognition of dichotic syllables relies on a previously identified process, indicating that the process is better labelled auditory linguistic than auditory lexical and suggesting that lexical status may be irrelevant to auditory language asymmetries. Also, a word naming task is found to produce visual field asymmetry because of a stimulus encoding (visual lexical) process, with no clear evidence found of influence from asymmetric response processes. Taken together, the full set of lateralized processes appear to show high degrees of modality specificity and mutual independence (modularity).