Contour detectionthreshold: repeatability and learning with 'contour cards' PHILIPPA M. PENNEFATHER 1,* ARVIND CHANDNA 1, ILONA KOVACS 2, URI POLAT 3 and ANTHONY M. NORCIA 4 1 Alder Hey Children's Hospital, Eaton Road, Liverpool, L12 2AP, UK 2 Laboratory of Vision Research, Rutgers University
matched for the detectionthreshold, on visual target detection. These effects were evident in comparisons between cued and uncued conditions, as well as in tasks that compared the effects of valid vs. invalid cues. * These authors made an equal contribution to the work. ** To whom correspondence should
The restricted operational space of dynamic driving simulators requires the implementation of motion cueing algorithms that tilt the simulator cabin to reproduce sustained accelerations. In order to avoid conflicting inertial cues, the tilt rate is limited below drivers’ perceptual thresholds, which are typically derived from the results of classical vestibular research, where additional sensory cues to self-motion are removed. These limits might be too conservative for an ecological driving simulation, which provides a variety of complex visual and vestibular cues as well as demands of attention which vary with task difficulty. We measured roll rate detection threshold in active driving simulation, where visual and vestibular stimuli are provided as well as increased cognitive load from the driving task. Here thresholds during active driving are compared with tilt rate detection thresholds found in the literature (passive thresholds) to assess the effect of the driving task. In a second experiment, these thresholds (active versus passive) are related to driving preferences in a slalom driving course in order to determine which roll rate values are most appropriate for driving simulators so as to present the most realistic driving experience. The results show that detection threshold for roll in an active driving task is significantly higher than the limits currently used in motion cueing algorithms, suggesting that higher tilt limits can be successfully implemented to better optimize simulator operational space. Supra-threshold roll rates in the slalom task are also rated as more realistic. Overall, our findings indicate that increasing task complexity in driving simulation can decrease motion sensitivity allowing for further expansion of the virtual workspace environment.
Many studies have investigated interactions in the processing of tactile stimuli across different fingers. However, the precise time-scale of these interactions when stimuli arrive on opposite sides of the body remains uncertain. Specifically, it is not clear how tactile stimulation of different fingers of the same and different hands can interact with each other. The aim of the present study was to address this issue using a novel approach combining the QUEST threshold estimation method with single pulse TMS (spTMS). First, QUEST was used in a two-interval forced-choice design in order to establish threshold for detecting a 200 ms, 100 Hz sinusoidal vibration applied to the index fingertip (target finger threshold). This was done either when the target was presented in isolation, or concurrently with a distractor stimulus on another finger of the same or a different hand. Second, the same participants underwent a series of MRI scans (localisers) to produce somatotopic maps of SI and SII cortices. These maps were used to stimulate over SI with spTMS during a subsequent behavioural task, with the aim of modulating the behavioural interactions between the different fingers. The results showed that the threshold for detecting the target was lower when it was presented in isolation, as compared to when a concurrent distractor was present. Moreover, detection thresholds varied as a function of the distractor finger stimulated. The differential effect of the distractor finger on target detection thresholds is consistent with the segregation of different fingers in early somatosensory processing, from the periphery to SI.
Temporal structure in the environment often has predictive value for anticipating the occurrence of forthcoming events. In this study we compared the influence of two types of predictive temporal information on auditory perception: (1) intrinsic temporal rhythmicity of an auditory stimulus stream and (2) temporally-predictive visual cues. We hypothesized that combining predictive temporal information within- and across-modality would improve auditory detection, beyond the advantage provided by each information source alone. We presented streams of tones at either increasing or decreasing intensities until participants reported that they could hear/no longer hear the tones. Tones were presented in either rhythmic or random sequences and were preceded by a temporally predictive visual flash in half of the trials. We show that detection thresholds are lower for rhythmic (vs. random) and audiovisual (vs. auditory-only) presentation, and that this effect is additive for rhythmic audiovisual presentation in both paradigms. These behavioral results suggest that both types of temporal information are used in parallel to prepare the perceptual system for upcoming stimuli and to optimally interact with the environment. Our findings underscore the flexibility and proactivity of the perceptual system which uses these temporal contextual factors combined to anticipate upcoming events and process them optimally.
How the body is represented in the brain has been an important topic of investigation for over a hundred years, with neurological, philosophical and physiological implications. Tactile processing, at even the lowest level, including localization, detection thresholds and two-point discrimination thresholds, turns out to depend on factors other than the cutaneous receptors. How these properties are affected and by what, can give insight into how the body is represented in the brain. Distortions in localization related to gaze direction suggest spatial coding in multiple reference frames. Distortions in detection and two-point discrimination thresholds related to alteration in perceived body shape indicate distortions in the relative size of different parts of the representation — perhaps related to receptive field changes in a cortical map. I will review several recent studies that together demonstrate that the body’s representation in the brain can be matched to various task requirements and that can be dynamically updated to respond to changes in posture and perceived body dimensions.
Sound localization is a multisensory process consisting not only of hearing, but also of self-motion perception. A large number of studies have shown that the listener’s head movement, particularly horizontal rotation, effectively improves sound localization acuity (Wallach, 1939; Thurlow, 1967; Kawaura, 1989; etc.). However, research into sound localization during head rotation is scarce. Thus, the multisensory process underlying sound localization remains unclear.
In the present study, we directly investigated the minimum audible angle (MAA) — the detection threshold needed for the listener to localize sounds at different positions — at the front during horizontal head rotation. A sound stimulus (30-ms noise burst) was presented from a loudspeaker of a circular array (r = 1.1 m), with a loudspeaker separation of 2.5 degrees. The listener, sitting at the center of the circle, was asked to answer whether the sound stimulus was presented from the left or right of the subjective front (2AFC). We considered two listening conditions, static and dynamic. In the static condition, listeners were asked to keep their heads still. Meanwhile, for the dynamic condition, listeners were asked to rapidly rotate their heads; the test stimulus was triggered during head movement. Sound stimuli were presented from a randomly selected loudspeaker out of a subset of 13 centered at the listener’s physical front at the time of stimulus presentation. Results showed the MAA to deteriorate significantly in the dynamic condition. This implies that the improvements in sound localization due to head motion could be explained by the multiple-look model (Viemeister and Wakefield, 1991).
detectionthresholds for a Gabor patch superimposed on this line and whether these effects depend on the orientation, spatial frequency and phase of the Gabor elements. Employing a 2AFC method with a staircase procedure we measured contrast detectionthresholds and varied the orientation, spatial frequency