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1. Mirror-Brush Illusion: Creating phantom tactile percepts on intact limbs

   https://doi.org/10.1109/TOH.2023.3279012  

   Singhala, Mohit; Brown, Jeremy D. (January 2023, IEEE Transactions on Haptics)

   Haptic illusions provide unique insights into how we model our bodies separate from our environment. Popular illusions like the rubber-hand illusion and mirror-box illusion have demonstrated that we can adapt the internal representations of our limbs in response to visuo-haptic conflicts. In this manuscript, we extend this knowledge by investigating to what extent, if any, we also augment our external representations of the environment and its action on our bodies in response to visuo-haptic conflicts. Utilizing a mirror and a robotic brushstroking platform, we create a novel illusory paradigm that presents a visuo-haptic conflict using congruent and incongruent tactile stimuli applied to participants' fingers. Overall, we observed that participants perceived an illusory tactile sensation on their visually occluded finger when seeing a visual stimulus that was inconsistent with the actual tactile stimulus provided. We also found residual effects of the illusion after the conflict was removed. These findings highlight how our need to maintain a coherent internal representation of our body extends to our model of our environment. 

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2. Electrically-evoked referred sensations induce embodiment of rubber limb

   https://doi.org/10.1177/20556683231183633  

   Nguyen, Anthony; Draggoo, Brooke; Tobias, Brooklyn; DuBose, Payton; Polasek, Katharine (January 2023, Journal of Rehabilitation and Assistive Technologies Engineering)

   Introduction Electrical stimulation is increasingly relevant in a variety of medical treatments. In this study, the quality of referred sensations evoked using surface electrical stimulation was evaluated using the rubber hand and foot illusions. Methods The rubber hand and foot illusions were attempted under 4 conditions: (1) multi-location tapping; (2) one-location tapping; (3) electrical stimulation of sensation referred to the hand or foot; (4) asynchronous control. The strength of each illusion was quantified using a questionnaire and proprioceptive drift, where a stronger response suggested embodiment of the rubber limb. Results 45 able-bodied individuals and two individuals with amputations participated in this study. Overall, the illusion evoked by nerve stimulation was not as strong as illusions evoked by physically tapping but stronger than the control illusion. Conclusion This study has found that the rubber hand and foot illusion can be performed without touching the distal limb of the participant. Electrical stimulation that produced referred sensation in the distal extremity was realistic enough to partially incorporate the rubber limb into a person’s body image. 

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3. Radial Bias Alters Perceived Object Orientation

   https://doi.org/10.1177/09567976221110243  

   Menceloglu, Melisa; Nakayama, Ken; Song, Joo-Hyun (October 2022, Psychological Science)

   Orientation sensitivity is a fundamental property of the visual system, but not all orientations are created equal. For instance, radially oriented stimuli, aligned with a line intersecting the center of gaze, produce greater activity throughout the visual cortex and are associated with greater perceptual sensitivity compared with other orientations. Here, we discuss a robust visual illusion that is likely related to this preference. Using a continuous response measure, participants ( N = 36 adults) indicated the gap position in a peripheral Landolt C placed in one of eight orientations and eight locations along four meridians (vertical, horizontal, 45°, 135°). The error distributions revealed that the perceived gap was attracted toward the radial axis. For instance, the gap in a regular C would often be wrongly perceived as tilted 45° corresponding to the oblique meridian where it was placed. These findings demonstrate an unsuspected early-vision influence on the perceived orientation of an object. 

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4. Quantifying VR cybersickness using EEG

   https://doi.org/10.1007/s10055-021-00517-2  

   Krokos, Eric; Varshney, Amitabh (May 2021, Virtual Reality)

   null (Ed.)

   Current techniques for characterizing cybersickness (visually induced motion sickness) in virtual environments rely on qualitative questionnaires. For interactive graphics to create visual experiences that enhance the illusion of presence while mitigating cybersickness, interactive measures are needed to characterize cybersickness. In this paper, we acquire EEG signals from participants as they experience vection-induced cybersickness and compare those signals to a baseline. Our study shows that there is a correlation between the participant-reported cybersickness (as measured by movements of a joystick) and brain EEG signals. Through independent component analysis, we separate those signals which are a result of cybersickness from other sources (such as eye blinks). Our user study finds that there is a highly correlative and statistically significant Delta- (1.0–4.0 Hz), Theta- (4.0–7.0 Hz), and Alpha-wave (7.0–13.0 Hz) increase associated with cybersickness in immersive virtual environments across participants. Establishing a strong correlation between cybersickness and EEG-measured brain activity provides us with the first step toward interactively characterizing and mitigating cybersickness in virtual environments. 

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5. Rapid Learning and Long-term Memory in the Speech-to-song Illusion

   https://doi.org/10.1525/mp.2024.41.5.348  

   Kubit, Benjamin M; Deng, Christine; Tierney, Adam; Margulis, Elizabeth H (June 2024, Music Perception: An Interdisciplinary Journal)

   The speech-to-song illusion is a perceptual transformation in which a spoken phrase initially heard as speech begins to sound like song across repetitions. In two experiments, we tested whether phrase-specific learning and memory processes engaged by repetition contribute to the illusion. In Experiment 1, participants heard 16 phrases across two conditions. In both conditions, participants heard eight repetitions of each phrase and rated their experience after each repetition using a 10-point scale from “sounds like speech” to “sounds like song.” The conditions differed in whether the repetitions were heard consecutively or interleaved such that participants were exposed to other phrases between each repetition. The illusion was strongest when exposures to phrases happened consecutively, but phrases were still rated as more song-like after interleaved exposures. In Experiment 2, participants heard eight consecutive repetitions of each of eight phrases. Seven days later, participants were exposed to eight consecutive repetitions of the eight phrases heard previously as well as eight novel phrases. The illusion was preserved across a delay of one week: familiar phrases were rated as more song-like in session two than novel phrases. The results provide evidence for the role of rapid phrase-specific learning and long-term memory in the speech-to-song illusion. 

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