[Endogenous and Exogenous Attention in Alzheimer Type of Dementia: Effect of Target Position]

Endogenous attention (EnA) is an ability in goal-driven processes, controlled by top-down mechanisms and exogenous attention (ExA) is an ability in stimulus-driven processes, controlled by bottomup mechanisms. In the present research, it was aimed to investigate in Alzheimer's disease (AD) the EnA and ExA processes in relation to target position (right/left) by using the Spatial Cueing Paradigm (SCP).

The study was conducted with the participants of 65-90 year age range, consisting of 14 female and 14 male (n=28) participants diagnosed with AD and 12 female and 12 male (n=24) healthy volunteers as controls. The group variable (AD, Control) was tested on the intergroup basis; and the attention type (EnA, ExA), trial type (valid /VT+ and invalid/ VT-) and the target position (left/right) variables were tested on the intra-subject basis (within subject design). Two separate factorial ANOVAs were conducted for mean reaction time and accuracy measures obtained from SCP.

In comparison to the control group, the AD group participants gave slow and wrong reactions to stimuli for EnA and ExA. The AD group responses were faster in the VT+s and more accurate in the VT-s to stimuli on the left as compared to those on the right; and the responses of AD patients to the stimuli on the left as compared to those on the right was more accurate in VT-s under ExA condition.

AD causes impairment of EnA and ExA. Faster reactions by AD participants to the target on the left in VT+s and more accurate reactions to the target on the left in VT-s are in agreement with reports in the literature on the lateralization of visual-spatial attention (VSA) in the right hemisphere. In this study, also in agreement with previous reports, lateralization in AD was noted in favour of the stimuli on the left in ExA.