Seeing the World as it is: Mimicking Veridical Motion Perception in Schizophrenia Using Non-invasive Brain Stimulation in Healthy Participants

Abstract

Schizophrenia (Sz) is a mental health disorder characterized by severe cognitive, emotional, social, and perceptual deficits. Visual deficits are found in tasks relying on the magnocellular/dorsal stream. In our first experiment we established deficits in global motion processing in Sz patients compared to healthy controls. We used a novel task in which background optic flow produces a distortion of the apparent trajectory of a moving stimulus, leading control participants to provide biased estimates of the true motion trajectory under conditions of global stimulation. Sz patients were significantly less affected by the global background motion, and reported trajectories that were more veridically accurate than those of controls. In order to study the mechanism of this effect, we performed a second experiment where we applied transcranial electrical stimulation over area MT+ to selectively modify global motion processing of optic flow displays in healthy participants. Cathodal and high frequency random noise stimulation had opposite effects on trajectory perception in optic flow. The brain stimulation over a control site and in a control task revealed that the effect of stimulation was specific for global motion processing in area MT+. These findings both support prior studies of impaired early visual processing in Sz and provide novel approaches for measurement and manipulation of the underlying circuits.

Keywords: MT+; Motion perception; Schizophrenia; Transcranial electrical stimulation.

Fig. 1

Stimuli. a Global task. Participants observed a radial optic flow field and a single upward moving red dot (probe) inside 1.3° radius aperture within the global optic flow field. Their task was to judge the perceived trajectory of an upward moving probe in a radial flow field. b Local Task. Inside a small 1.3° radius aperture participants observed a radial optic flow field and an upward moving red probe. c Response Gauge. Participants were indicating perceived direction of the probe by positioning the arrow gauge. The discrepancy between the onscreen probe movement and the perceived probe movement was used to determine the relative tilt

Fig. 2

Behavioural results. a The relative tilt for global and local flow fields in control participants and schizophrenic patients (Sz). Sz patients show significantly reduced global tilt compared to control participants. Error bars indicate standard error of mean (SEM). b Correlations between global task performance in Sz patients and (left panel) perceptual rotation threshold (proportion coherent dots) and (right panel) score on Block Design test

Fig. 3

TES results. a MT+ region and TES electrode montage. Anodal and cathodal refer to tDCS stimulation. HF-RNS represent high frequency random-noise stimulation. b ATL region and TES electrode montage. Anodal and cathodal refer to tDCS stimulation. HF-RNS represent high frequency random-noise stimulation. Each bar represents the TES modulation of relative tilt effect for global and local optic flow fields. Error bars indicate standard error of mean (SEM) adjusted to reflect the between-condition variance used in repeated-measure designs (Loftus and Mason 1994). MT cortical middle temporal area, ATL anterior temporal lobe, TES transcranial electrical stimulation, HF-RNS high frequency random noise stimulation

Fig. 4

Effect sizes of global relative tilt following TES stimulation

Fig. 5

Model of transcranial direct current stimulation (tDCS) current. Red-yellow colours indicate increased magnitude of the total electric field due to tDCS. Left panel displays right MT+ stimulation, while the right panel highlights stimulation within the right anterior temporal lobes