Eliana M. Klier

Optimal multisensory decision-making in a reaction-time task

Humans and animals can integrate sensory evidence from various sources to make decisions in a statistically near-optimal manner, provided that the stimulus presentation time is fixed across trials. Little is known about whether optimality is preserved when subjects can choose when to make a decision (reaction-time task), nor when sensory inputs have time-varying reliability. Using a reaction-time version of a visual/vestibular heading discrimination task, we show that behavior is clearly sub-optimal when quantified with traditional optimality metrics that ignore reaction times. We created a computational model that accumulates evidence optimally across both cues and time, and trades off accuracy with decision speed. This model quantitatively explains subjectss choices and reaction times, supporting the hypothesis that subjects do, in fact, accumulate evidence optimally over time and across sensory modalities, even when the reaction time is under the subjects control. DOI: http://dx.doi.org/10.7554/eLife.03005.001

Reaching the Limit of the Oculomotor Plant: 3D Kinematics after Abducens Nerve Stimulation during the Torsional Vestibulo-Ocular Reflex

Accumulating evidence shows that the oculomotor plant is capable of implementing aspects of three-dimensional kinematics such as Listings law and the half-angle rule. But these studies have only examined the eye under static conditions or with movements that normally obey these rules (e.g., saccades and pursuit). Here we test the capability of the oculomotor plant to rearrange itself as necessary for non-half-angle behavior. Three monkeys (Macaca mulatta) fixated five vertically displaced targets along the midsagittal plane while sitting on a motion platform that rotated sinusoidally about the naso-occipital axis. This activated the torsional, rotational vestibulo-ocular reflex, which exhibits a zero-angle or negative-angle rule (depending on the visual stimulus). On random sinusoidal cycles, we stimulated the abducens nerve and observed the resultant eye movements. If the plant has rearranged itself to implement this non-half-angle behavior, then stimulation should reveal this behavior. On the other hand, if the plant is only capable of half-angle behavior, then stimulation should reveal a half-angle rule. We find the latter to be true and therefore additional neural signals are likely necessary to implement non-half-angle behavior.