M.Sc Thesis

M.Sc StudentGruman Ayelet
SubjectBehavioral and Electrophysiological Measures in a Cued
Attention Task Combining Response Inhibition,
Response Selection, and Information
Processing from Competing Chan
DepartmentDepartment of Medicine
Supervisors PROF. Shimon Marom
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Impaired executive functions are related to a number of psychiatric disorders, especially mechanisms connected to response inhibition, cognitive conflict, and selective attention.

The main objective for this research was to develop a new cued attention task that will enable to examine attention functions and response selection, simultaneously, through variable difficulty levels. We created an auditory task, based on a set of 3 dimensioned auditory stimulus: stimuli location (right / left), speaker's voice (man's voice / woman's voice), word meaning (right / left). Due to switching instructions given to the subject throughout the task, these stimuli received different context, and were therefore processed differently. The new task combines aspects of known attention tasks, and differentiating the aspects is based on the stimuli's switching requirements.

Nineteen (10 men and 9 women), healthy, right-handed, native Hebrew speakers, participated in this study. Behavioral measurements were taken in addition to AEPs that were recorded by 61 electrodes in order to examine data processing.

The task produced competition between two processing channels (stimuli location dimension and word meaning dimension) and creates auditory stroop effect. Stroop effect manifested in longer reaction times and greater amplitude for LN and N1 components when stimulus dimensions were incongruent compared to congruent stimuli. The reason for the reflection of stroop effect is the physical mismatch between stimuli dimensions, and the higher conflict state of processing in the incongruent stimuli. On the other hand, the task was not reliable enough to report response inhibition purely, probably as a result of the task's complexity. The new auditory cued attention task did not reveal ear advantage, and the results received from comparing the responses between stimulus heard in right ear or left ear were not consistent. The task was found suitable to study voice advantage: behavioral results showed a longer mean reaction time for a stimulus heard in a woman's voice than in a man's voice. Through the use of switching instructions throughout the task we created attention switching, and showed that the task stimulates different processing types (referring to the same stimuli) and allows examination of the attention mechanism in terms of "early selection" compared to "late selection", relating to two of the stimulus dimensions: location and speaker's gender.

Results imply that in the early selection process, attention is used for prevention or reduction of the processing of an irrelevant stimulus, while in late selection, attention is used for response selection to the relevant stimulus.

 In addition, by comparing the results to different stimulus dimensions, influenced by diverting attention, we found that the competing auditory stimulus dimensions (location, speaker's gender) affected the selective attention mechanism.

In summary, the new task combines an array of different cognitive abilities in which we can test varied complexities and difficulty levels depending on varying circumstances. In addition, the task enables control of the different circumstances according to stimulus meaning and thereby assessing each functional aspect separately. Therefore, the new task can be used as a diagnostic and research tool for executive functions.