Accounting for endogenous effects in decision‐making with a non‐linear diffusion decision model
(2023)
The Drift‐Diffusion Model (DDM) is widely accepted for two‐alternative forced‐choice decision paradigms thanks to its simple formalism and close fit to behavioral and neurophysiological data. However, this formalism presents strong limitations in capturing inter‐trial dynamics at the single‐ trial level and endogenous influences. We propose a novel model, the non‐linear Drift‐Diffusion Model (nl‐DDM), that addresses these issues by allowing the existence of several trajectories to the decision boundary. We show that the non‐linear model performs better than the drift‐diffusion model for an equivalent complexity. To give better intuition on the meaning of nl‐DDM parameters, we compare the DDM and the nl‐DDM through correlation analysis. This paper provides evidence of the functioning of our model as an extension of the DDM. Moreover, we show that the nl‐DDM captures time effects better than the DDM. Our model paves the way toward more accurately analyzing across‐trial variability for perceptual decisions and accounts for peri‐stimulus influences.
The integrative experiment design proposal currently only relates to group results, but downplays individual differences between participants, which may nevertheless be substantial enough to constitute a relevant dimension in the design space. Excluding the individual participant in the integrative design will not solve all problems mentioned in the target article, because averaging results may obscure the underlying mechanisms.
One of the major challenges for computational models of timing and time perception is to identify a neurobiological plausible implementation that predicts various behavioral properties, including the scalar property and retrospective timing. The available timing models primarily focus on the scalar property and prospective timing, while virtually ignoring the computational accessibility. Here, we first selectively review timing models based on ramping activity, oscillatory pattern, and time cells, and discuss potential challenges for the existing models. We then propose a multifrequency oscilla- tory model that offers computational accessibility, which could account for a much broader range of timing features, including both retrospective and prospective timing.
Integration of multi-sensory signals is normally required to infer the properties and states of the external world and of the own body. This applies also to vestibular signals, which, when activated are naturally accompanied by other sensory or self-generated signals. Here, we review computational schemes and normative principles that have been proposed to achieve meaningful signal fusion that allows perception and action in the face of uncertain information.
Objective: We are still lacking a pathophysiological mechanism for functional disorders explaining the emergence and manifestation of characteristic, severely impairing bodily symptoms like chest pain or dizziness. A recent hypothesis based on the predictive coding theory of brain function suggests that in functional disorders, internal expectations do not match the actual sensory body states, leading to perceptual dysregulation and symptom perception. To test this hypothesis, we investigated the account of internal expectations and sensory input on gaze stabilization, a physiologically relevant parameter of gaze shifts, in functional dizziness.
Methods: We assessed gaze stabilization in eight functional dizziness patients and 11 healthy controls during two distinct epochs of large gaze shifts: during a counter- rotation epoch (CR epoch), where the brain can use internal models, motor planning, and resulting internal expectations to achieve internally driven gaze stabilization; and during an oscillation epoch (OSC epoch), where, due to terminated motor planning, no movement expectations are present, and gaze is stabilized by sensory input alone.
Results: Gaze stabilization differed between functional patients and healthy controls only when internal movement expectations were involved [F(1,17) = 14.63, p = 0.001, and partial η2 = 0.463]: functional dizziness patients showed reduced gaze stabilization during the CR (p = 0.036) but not OSC epoch (p = 0.26).
Conclusion: While sensory-driven gaze stabilization is intact, there are marked, well- measurable deficits in internally-driven gaze stabilization in functional dizziness pointing at internal expectations that do not match actual body states. This experimental evidence supports the perceptual dysregulation hypothesis of functional disorders and is an important step toward understanding the underlying pathophysiology.
Image motion with color contrast suffices to elicit an optokinetic reflex in Xenopus laevis tadpoles
(2021)
The optokinetic reflex is a closed-loop gaze-stabilizing ocular motor reaction that minimizes residual retinal image slip during vestibulo-ocular reflexes. In experimental isolation, the reflex is usually activated by motion of an achromatic large-field visual background with strong influence of radiance contrast on visual motion estimation and behavioral performance. The presence of color in natural environments, however, suggests that chromatic cues of visual scenes provide additional parameters for image motion detection. Here, we employed Xenopus laevis tadpoles to study the influence of color cues on the performance of the optokinetic reflex and multi-unit optic nerve discharge during motion of a large-field visual scene. Even though the amplitude of the optokinetic reflex decreases with smaller radiance contrast, considerable residual eye movements persist at the ‘point of equiluminance’ of the colored stimuli. Given the color motion preferences of individual optic nerve fibers, the underlying computation potentially originates in retinal circuits. Differential retinal ganglion cell projections and associated ocular motor signal transformation might further reinforce the color dependency in conceptual correspondence with head/body optomotor signaling. Optokinetic reflex performance under natural light conditions is accordingly influenced by radiance contrast as well as by the color composition of the moving visual scene.
Methods: Body sway was analyzed by measuring the center of pressure (CoP) in 10 healthy participants on a pressure-sensitive treadmill during standing and walking at 0.4 or 0.8 m/s. Continuous SVS (0–25 Hz; peak amplitude at±4.5 mA) was delivered by a bipolar binaural electrode configuration over the mastoid processes to evoke postural responses in the roll plane. Time-dependent coherence between SVS and medio-lateral body sway was analyzed to examine the dynamic impact of vestibular cues during locomotion. HMP was estimated using a previously established model (MacNeilage and Glasauer, 2017).
Results: SVS-CoP coherence decreased from standing to slow walking and further decreased with increasing locomotor speed (p< 0.001). Correspondingly, HMP increased with faster locomotion (p= 0.001). SVS-CoP coherence depended on the gait cycle phase with two distinct peaks occurring at 25 …
Surface filling-in and contour interpolation contribute independently to Kanizsa figure formation
(2018)
Both, the hippocampal formation and the neocortex are contributing to declarative memory, but their functional specialization remains unclear. We investigated the differential contribution of both memory systems during free recall of word lists. In total, 21 women and 17 men studied the same list but with the help of different encoding associations. Participants associated the words either sequentially with the previous word on the list, with spatial locations on a well-known path, or with unique autobiographical events. After intensive rehearsal, subjects recalled the words during functional magnetic resonance imaging (fMRI). Common activity to all three types of encoding associations was identified in the posterior parietal cortex, in particular in the precuneus. Additionally, when associating spatial or autobiographical material, retrosplenial cortex activity was elicited during word list recall, while hippocampal activity emerged only for autobiographically associated words. These findings support a general, critical function of the precuneus in episodic memory storage and retrieval. The encoding-retrieval repetitions during learning seem to have accelerated hippocampus-independence and lead to direct neocortical integration in the sequentially associated and spatially associated word list tasks. During recall of words associated with autobiographical memories, the hippocampus might add spatiotemporal information supporting detailed scenic and contextual memories.
The vestibular sensors in the inner ear measure head movement with respect to an inertial frame of reference. The chapter describes the principles of measurement of the vestibular sensors, the physical stimuli that are measured, and specific issues that require central processing. An overview about so-called artificial vestibular stimuli that mimic the effect of natural head movement is provided.