Central and Divided Visual Field Presentation of Emotional Images to Measure Hemispheric Differences in Motivated Attention.

Two dominant theories on lateralized processing of emotional information exist in the literature. One theory posits that unpleasant emotions are processed by right frontal regions, while pleasant emotions are processed by left frontal regions. The other theory posits that the right hemisphere is more specialized for the processing of emotional information overall, particularly in posterior regions. Assessing the different roles of the cerebral hemispheres in processing emotional information can be difficult without the use of neuroimaging methodologies, which are not accessible or affordable to all scientists. Divided visual field presentation of stimuli can allow for the investigation of lateralized processing of information without the use of neuroimaging technology. This study compared central versus divided visual field presentations of emotional images to assess differences in motivated attention between the two hemispheres. The late positive potential (LPP) was recorded using electroencephalography (EEG) and event-related potentials (ERPs) methodologies to assess motivated attention. Future work will pair this paradigm with a more active behavioral task to explore the behavioral impacts on the attentional differences found.

Valence and arousal influence the late positive potential during central and lateralized presentation of images.

The motivated attention network is believed to be the system that allocates attention toward motivationally relevant, emotional stimuli in order to better prepare an organism for action [Lang, P. J., Bradley, M. M., & Cuthbert, B. N. (1997). Motivated attention: Affect, activation, and action. In P. J. Lang, R. F. Simons, M. Balaban, & R. Simons (Eds.), Attention and orienting: Sensory and motivational processes (pp. 97-135). Psychology Press]. The late positive potential (LPP), an event-related potential (ERP) that is a manifestation of the motivated attention network, has not been found to reliably differentiate the valence of emotionally relevant stimuli. In two studies, we systematically varied epoch, stimulus arousal, stimulus valence, and hemisphere of presentation (Study 2) to investigate valence effects in the LPP. Both central and divided visual field presentations of emotional stimuli found the LPP to be sustained in later windows for high-arousing unpleasant images compared to pleasant images. Further, this effect was driven by sustained LPP responses following left hemisphere presentations of unpleasant stimuli compared to right. Findings are discussed regarding hemispheric processing of emotion and how lateralized emotion processes might contribute to psychopathology.

Depression reduces perceptual sensitivity for positive words and pictures.

There is evidence of maladaptive attentional biases for lexical information (e.g., Atchley, Ilardi, & Enloe, 2003; Atchley, Stringer, Mathias, Ilardi, & Minatrea, 2007) and for pictographic stimuli (e.g., Gotlib, Krasnoperova, Yue, & Joormann, 2004) among patients with depression. The current research looks for depressotypic processing biases among depressed out-patients and non-clinical controls, using both verbal and pictorial stimuli. A d' measure (sensitivity index) was used to examine each participant's perceptual sensitivity threshold. Never-depressed controls evidenced a detection bias for positive picture stimuli, while depressed participants had no such bias. With verbal stimuli, depressed individuals showed specific decrements in the detection of positive person-referent words (WINNER), but not with positive non-person-referent words (SUNSHINE) or with negative words. Never-depressed participants showed no such differences across word types. In the current study, depression is characterised both by an absence of the normal positivistic biases seen in individuals without mood disorders (consistent with McCabe & Gotlib, 1995), and by a specific reduction in sensitivity for person-referent positive information that might be inconsistent with depressotypic self-schemas.

Offset masking in a divided visual field study.

A problem in divided visual field studies (especially those using event-related potentials as a dependent measure) is the large number of horizontal eye movements participants make during experimental trials. Past attention research suggests that eye movements to lateralised targets should be significantly reduced using a dynamic, offset mask, causing a reduction in attentional capture. The current study attempted to replicate past divided visual field language studies using offset masking procedures. Using a basic offset procedure, eye movements were not reduced in Experiment 1. However, Experiment 2 did show a significant reduction in eye movements using a new dynamic offset masking procedure. Low accuracy rates were a concern throughout. In conclusion, horizontal eye movements can be reduced with a dynamic offset procedure but the low accuracy rates and the inconsistent behavioural findings throughout the study suggest that further study and refinement of the paradigm is needed.