Biology subjects

Shenyan, O.

Publications and source records attributed to Shenyan, O..

3 recordsLinked to original sources

bioRxiv2025

Protective effect of prior knowledge in ageing

Visual perception depends on both sensory input and prior knowledge, and the quality of these information sources changes across the lifespan. As people age, accumulated knowledge, and its influence on perception, tend to increase, while declines in low-level visual functions reduce input quality and bias perception toward prior information. Yet, the combined effects of these changes on higher-level visual perception remain unclear, partly because concurrent cognitive decline may complicate the use of stored knowledge. In this study, we examined how prior knowledge shapes visual perception in younger (<40 years) and older (>60 years) adults using ambiguous two-tone images, whose recognition depends on prior knowledge. Providing participants with the original photographs used to generate the two-tones triggered perceptual reorganisation, improving recognition in both groups. Although older adults recognised fewer two-tones overall - a pattern linked to reduced visual acuity - they showed a comparable benefit from prior knowledge when cued. These findings suggest that, despite age-related sensory decline, the ability to draw on prior knowledge remains robust in older adulthood and may help preserve perceptual function.

neuroscience↗

bioRxiv2025

Reduced susceptibility to experimentally-induced complex visual hallucinations with age

Visual hallucinations occur across many clinical conditions, but can also be induced experimentally in healthy individuals, using high-frequency flicker (Ganzflicker) and sensory deprivation (Ganzfeld). It is unclear how hallucinatory proneness changes across the lifespan, with prior questionnaire-based studies showing mixed results. As factors such as multi-sensory acuity loss and relatively increased reliance on prior knowledge may increase as we age, and these are considered risk factors for hallucination proneness, we hypothesised that reported decreases in hallucinations might reflect stigma-related underreporting. We therefore sought to measure hallucination proneness in 44 healthy adults spanning the adult lifespan (younger age group; n=22; age 19-39 years, mean 27.2 {+/-} 5.5; older age group n=22; age 59-79 years, mean 68.0 {+/-} 5.8), quantifying the tendency to experience complex and simple hallucinations in an experimental environment designed to elicit hallucinations. We find that reports of complex hallucinations (those representing objects, scenes, etc) are lower in older adults than in younger adults, both in real time and retrospectively. None of our measured cognitive or sensory measures (visual acuity, contrast sensitivity, perceptual reorganisation, imagery vividness, memory inhibition, and suggestibility) mediate this relationship. We conclude that reduced complex hallucination proneness appears normative in ageing, and that experiencing hallucinations in older individuals may signal underlying pathology.

neuroscience↗

bioRxiv2023

Flicker and Ganzfeld induced visual hallucinations differ in frequency and content

Hallucinatory experiences, defined as perception in the absence of external stimuli, can occur in both pathological and non-pathological states and can be broadly phenomenologically divided into those of a simple and a complex nature. Non-pathological visual hallucinations can be induced experimentally using a variety of stimulation conditions. To assess whether these techniques drive a shared underlying hallucinatory mechanism, despite these differences, we compared two methods: flicker and perceptual deprivation (Ganzfeld). Specifically, we measured the frequency and complexity of the hallucinations produced by these techniques. We utilised button press, retrospective drawing, interviews, and questionnaires to quantify hallucinatory experience in 20 participants. With both experimental techniques, we found that simple hallucinations were more common than complex hallucinations. We also found that on average, flicker was more effective than Ganzfeld at eliciting a higher number of hallucinations, though Ganzfeld hallucinations were longer than flicker hallucinations. There was no interaction between experimental condition and hallucination complexity, suggesting that the increased bottom-up visual input in flicker increased both simple and complex hallucinations similarly. A correlation was observed between the total proportional time spent hallucinating in flicker and Ganzfeld, which was replicated in a retrospective questionnaire measure of experienced intensity, suggesting a shared hallucinatory mechanism between the two methodologies. We attribute these findings to a shared low-level core hallucinatory mechanism, such as excitability of visual cortex, which is amplified in flicker compared to Ganzfeld due to heightened bottom-up input.

neuroscience↗