Auditory speed processing in sighted and blind individuals

Multisensory experience is crucial for developing a coherent perception of the world. In this context, vision and audition are essential tools to scaffold spatial and temporal representations, respectively. Since speed encompasses both space and time, investigating this dimension in blindness allows deepening the relationship between sensory modalities and the two representation domains. In the present study, we hypothesized that visual deprivation influences the use of spatial and temporal cues underlying acoustic speed perception. To this end, ten early blind and ten blindfolded sighted participants performed a speed discrimination task in which spatial, temporal, or both cues were available to infer moving sounds’ velocity. The results indicated that both sighted and early blind participants preferentially relied on temporal cues to determine stimuli speed, by following an assumption that identified as faster those sounds with a shorter duration. However, in some cases, this temporal assumption produces a misperception of the stimulus speed that negatively affected participants’ performance. Interestingly, early blind participants were more influenced by this misleading temporal assumption than sighted controls, resulting in a stronger impairment in the speed discrimination performance. These findings demonstrate that the absence of visual experience in early life increases the auditory system’s preference for the time domain and, consequentially, affects the perception of speed through audition.

Effect of Repetitive Transcranial Magnetic Stimulation on a Target Moving in Front of a Static or Random Dynamic Visual Noise

Observers report seeing as slower a target disk moving in front of a static visual noise (SVN) background than the same object moving in front of a random dynamic visual noise (rDVN) background when the speed is the same. To investigate in which brain region (lower vs. higher visual areas) the background and the target signals might be combined to elicit this misperception, the transcranial magnetic stimulation (TMS) was delivered over the early visual cortex (V1/V2), middle temporal area (MT) and Cz (control site) while participants performed a speed discrimination task with targets moving in front of an SVN or an rDVN. Results showed that the TMS over MT reduced the perceived speed of the target moving in front of an SVN, but not when the target was moving in front of an rDVN background. Moreover, the TMS do not seem to interfere with encoding processing but more likely affected decoding processing in conditions of high uncertainty (i.e., when targets have similar speed).

Three-Dimensional Motion Perception: Comparing Speed and Speed Change Discrimination for Looming Stimuli

Judging the speed of objects moving in three dimensions is important in our everyday lives because we interact with objects in a three-dimensional world. However, speed perception has been seldom studied for motion in depth, particularly when using monocular cues such as looming. Here, we compared speed discrimination, and speed change discrimination, for looming stimuli, in order to better understand what visual information is used for these tasks. For the speed discrimination task, we manipulated the distance and duration information available, in order to investigate if participants were specifically using speed information. For speed change discrimination, total distance and duration were held constant; hence, they could not be used to successfully perform that task. For the speed change discrimination task, our data were consistent with observers not responding specifically to speed changes within an interval. Instead, they may have used alternative, arguably less optimal, strategies to complete the task. Evidence suggested that participants used a variety of cues to complete the speed discrimination task, not always solely relying on speed. Further, our data suggested that participants may have switched between cues on a trial to trial basis. We conclude that speed changes in looming stimuli were not used in a speed change discrimination task, and that naïve participants may not always exclusively use speed for speed discrimination.

Three-dimensional motion perception: comparing speed and speed change discrimination for looming stimuli

Judging the speed of objects moving in three dimensions is important in our everyday lives, because we interact with objects in a three-dimensional world. However, speed perception has been seldom studied for motion in depth, particularly when using monocular cues such as looming. Here, we compared speed discrimination, and speed change discrimination, for looming stimuli, to better understand what visual information is used for these tasks. For the speed discrimination task, we manipulated the distance and duration information available, to investigate if participants were specifically using speed information. For speed change discrimination, total distance and duration were held constant, hence they could not be used to successfully perform that task. We found speed change discrimination thresholds were consistently higher than those for speed discrimination. Evidence suggested that participants used a variety of cues to complete the speed discrimination task, not always solely relying on speed. Further, our data suggested that participants may switch between cues on a trial to trial basis. We conclude that speed change discrimination for looming is more difficult than speed discrimination, and that naїve participants may not always exclusively use speed for speed discrimination.

Adaptation to the Speed of Biological Motion in Autism

Autistic individuals often present atypicalities in adaptation—the continuous recalibration of perceptual systems driven by recent sensory experiences. Here, we examined such atypicalities in human biological motion. We used a dual-task paradigm, including a running-speed discrimination task (‘comparing the speed of two running silhouettes’) and a change-detection task (‘detecting fixation-point shrinkages’) assessing attention. We tested 19 school-age autistic and 19 age- and ability-matched typical participants, also recording eye-movements. The two groups presented comparable speed-discrimination abilities and, unexpectedly, comparable adaptation. Accuracy in the change-detection task and the scatter of eye-fixations around the fixation point were also similar across groups. Yet, the scatter of fixations reliably predicted the magnitude of adaptation, demonstrating the importance of controlling for attention in adaptation studies.

Discriminating tactile speed in absence of raised texture elements: Role of deformation and vibratory cues

Motion encoding in touch relies on multiple cues, such as displacements of traceable texture elements, friction-induced vibrations, and gross fingertip deformations by shear force. We evaluated the role of deformation and vibration cues in tactile speed discrimination. To this end, we tested the discrimination of speed of a moving smooth glass plate, and compared the precision of the responses when the same task was performed with a plate having a fine texture. Participants performed the task with and without masking vibrations. Speed discrimination was nearly as precise among the two surface types, as assessed by the steep slope of the psychometric function. Consistent with our previous work, high-frequency vibrations impaired the ability of the participants in discriminating surface speed. Results of the current study showed that it is possible to discriminate motion speed even in absence of a raised texture.HighlightsOn a smooth surface, humans are able to discriminate the speed of a moving surface by frictional motion cuesThe precision of speed discrimination is nearly the same with smooth and fine-textured surface typesHigh frequency vibrations impair the ability to discriminate speed of moving surfaces

Dysfunctional Default Mode Network during high speed discrimination in the elderly. Neuropsychological and driving simulator correlations.

Numerous daily tasks, including car driving, require fine visuospatial tuning. Onesuch visuospatial ability, speed discrimination, declines with aging but its neuralunderpinnings remain unknown. In this study, we use fMRI to explore the effect ofaging during a high speed discrimination task, along with a completeneuropsychological assessment and a simulated driving evaluation in order toexamine how they interact with each other. Beyond confirming that high speeddiscrimination performance is dimished in the elderly, we found that this deficit mightbe partly due to a lack of modulation in the activity and connectivity of the defaultmode network (DMN) in this age group, as well as an over-recruitment of frontal,basal ganglia and cerebellar regions, possibly as a compensatory mecanism. Thisneural pattern could also be translated to our participants’ cognitive and drivingsimulator performance, such that in young adults, a proper DMN modulationcorrelated with better neuropsychological scores and a driving profile, an effect thatseems to be lost in the elderly. These findings contribute to highlight the role of thedefault mode network on visuospatial tasks, how it is age-related and its impact on cognitive functioning and driving performance in a simulator.