Spatial and attentional influences on nonverbal magnitude discrimination in depressed and non-depressed individuals / by Stewart A. Madon.

Abstract

Numbers have been called the universal language. Yet the psychophysical properties of numerosity remain elusive, particularly as they relate to clinical disorders such as depression. It is known that the estimation and discrimination of magnitude remain a culturally unbiased phenomenon that could be used to negate the error associated with the use of linguistic or pictorial stimuli during assessments. Also, recent imaging studies have proposed that different processing streams are associated with the spatial perception of foreground and background image characteristics, with contextual binding of these two fields occurring in the right hippocampus. Using a novel three-dimensionally shadowed circularly concentric centersurround stimulus in which dot arrays were placed in either or both of the shadowed foreground and background fields, we hoped to ascertain whether depression can affect the performance on a magnitude estimation task. Changing dot arrays in either of the two fields across two time epochs, participants were required to accurately indicate which of the intervals had the greater number. In some blocks, a “red” coloured field was used to cue which of the two fields contained the changing dots. The inclusion of cue conditions allowed for the measurement of potential hippocampal and attentional dysfunctions in depressed individuals. Six depressed and 34 control (nondepressed) participants were recruited from psychology classes at Lakehead University. Dependent variables used to assess performance were Reaction Time (RT) and difference threshold (magnitude estimation accuracy). Our results showed that the depressed performed significantly worse than controls in overall accuracy, but that no RT differences were observed between the groups. Further, we noted some interesting increases in response latency relating to atypical vs. typical foreground/background arrangements. Finally, we found support for the theory that the dorsal visual stream can also process task-specific visual information typically associated with ventral visual pathway.

Study participants : Lakehead University Psychology students (Thunder Bay, Northwestern Ontario).