Humans can sense large numbers of objects in a box by touch alone.

Everyday experiences suggest that a container, such as a box of cereal, can convey pertinent information about the nature and quantity of its content. This study investigated how well people can judge large quantities of objects in a container through haptic perception. Stimuli consisted of plastic drinking straws cut to "small" (1.5 cm) or "big" (4.5 cm) pieces contained in plastic food containers. Participants performed both a magnitude estimation of the number of objects and a direct estimation of the proportion of the container perceived to be filled with objects. Overall, participants demonstrated considerable accuracy for both tasks and irrespective of the size of the content. Post-experiment interviews revealed three potential strategies. Participants either focused on the container's contents, the excess space in the container, or the perceived weight of the container (content).

Planning lane changes using advance visual and haptic information.

Taking a motor planning perspective, this study investigates whether haptic force cues displayed on the steering wheel are more effective than visual cues in signaling the direction of an upcoming lane change. Licensed drivers drove in a fixed-base driving simulator equipped with an active steering system for realistic force feedback. They were instructed to make lane changes upon registering a directional cue. Cues were delivered according to the movement precuing technique employing a pair of precues and imperative cues which could be either visual, haptic, or crossmodal (a visual precue with a haptic imperative cue, and vice versa). The main dependent variable was response time. Additional analyses were conducted on steering wheel angle profiles and the rate of initial steering errors. Conditions with a haptic imperative cue produced considerably faster responses than conditions with a visual imperative cue, irrespective of the precue modality. Valid and invalid precues produced the typical gains and costs, with one exception. There appeared to be little cost in response time or initial steering errors associated with invalid cueing when both cues were haptic. The results are consistent with the hypothesis that imperative haptic cues facilitate action selection while visual stimuli require additional time-consuming cognitive processing.

Humans can sense small numbers of objects in a box by touch alone.

Everyday experiences suggest that a container, such as a box of chocolate sprinkles, can convey pertinent information about the nature of its content. Despite the familiarity of the experience, we do not know whether people can perceive the number of objects in the container from touch alone and how accurately they can do so. In three experiments, participants handled containers holding between one and five objects and verbally estimated their number. Containers were small cardboard jewelry boxes, and objects were round beads of varying diameter and weight. Any useful visual and auditory cues were precluded. Experiment 1 demonstrated very accurate performance, provided the objects were of sufficient weight. Experiment 2 demonstrated that withholding information about the possible number of objects inside the container does not affect accuracy at a group level but does produce occasional overestimations at an individual level. Experiment 3 demonstrated that removing the weight cue leads to systematic underestimations but does not eliminate people's ability to distinguish between different numbers of objects in the container. This study contributes to a growing picture that container haptics is surprisingly capable.

Do whole-body vibrations affect spatial hearing?

To assist the human operator, modern auditory interfaces increasingly rely on sound spatialisation to display auditory information and warning signals. However, we often operate in environments that apply vibrations to the whole body, e.g. when driving a vehicle. Here, we report three experiments investigating the effect of sinusoidal vibrations along the vertical axis on spatial hearing. The first was a free-field, narrow-band noise localisation experiment with 5- Hz vibration at 0.88 ms(-2). The other experiments used headphone-based sound lateralisation tasks. Experiment 2 investigated the effect of vibration frequency (4 vs. 8 Hz) at two different magnitudes (0.83 vs. 1.65 ms(-2)) on a left-right discrimination one-interval forced-choice task. Experiment 3 assessed the effect on a two-interval forced-choice location discrimination task with respect to the central and two peripheral reference locations. In spite of the broad range of methods, none of the experiments show a reliable effect of whole-body vibrations on localisation performance. PRACTITIONER SUMMARY: We report three experiments that used both free-field localisation and headphone lateralisation tasks to assess their sensitivity to whole-body vibrations at low frequencies. None of the experiments show a reliable effect of either frequency or magnitude of whole-body vibrations on localisation performance.

Humans sense by touch the location of objects that roll in handheld containers.

Humans use active touch to gain behaviourally relevant information from their environment, including information about contained objects. Although most common, the perceptual basis of interacting with containers remains largely unexplored. The first aim of this study was to determine how accurately people can sense, by touch only, the location of a contained rolling object. Experiment 1 used tubes containing physical balls and demonstrated a considerable degree of accuracy in estimating the rolled distance. The second aim was to identify the relative effectiveness of the various available physical cues. Experiment 2 employed virtual reality technology to present, in isolation and in various combinations, the constituent haptic cues produced by a rolling ball, which are, the mechanical noise during rolling, the jolts from an impact with an internal wall, and the intensity and timing of the jolts resulting from elastic bounces. The rolling noise was of primary importance to the perceptual estimation task suggesting that the implementation of the laws of motion is based on an analysis of the ball's movement velocity. Although estimates became more accurate when the rolling and impact cues were combined, they were not necessarily more precise. The presence of elastic bounces did not affect performance.

Integration of vestibular and proprioceptive signals for spatial updating.

Spatial updating during self-motion typically involves the appropriate integration of both visual and non-visual cues, including vestibular and proprioceptive information. Here, we investigated how human observers combine these two non-visual cues during full-stride curvilinear walking. To obtain a continuous, real-time estimate of perceived position, observers were asked to continuously point toward a previously viewed target in the absence of vision. They did so while moving on a large circular treadmill under various movement conditions. Two conditions were designed to evaluate spatial updating when information was largely limited to either proprioceptive information (walking in place) or vestibular information (passive movement). A third condition evaluated updating when both sources of information were available (walking through space) and were either congruent or in conflict. During both the passive movement condition and while walking through space, the pattern of pointing behavior demonstrated evidence of accurate egocentric updating. In contrast, when walking in place, perceived self-motion was underestimated and participants always adjusted the pointer at a constant rate, irrespective of changes in the rate at which the participant moved relative to the target. The results are discussed in relation to the maximum likelihood estimation model of sensory integration. They show that when the two cues were congruent, estimates were combined, such that the variance of the adjustments was generally reduced. Results also suggest that when conflicts were introduced between the vestibular and proprioceptive cues, spatial updating was based on a weighted average of the two inputs.

Upper limits of auditory rotational motion perception.

Three experiments are reported, which investigated the auditory velocity thresholds beyond which listeners are no longer able to perceptually resolve a smooth circular trajectory. These thresholds were measured for band-limited noises, white noise, and harmonic sounds (HS), and in different acoustical environments. Experiments 1 and 2 were conducted in an acoustically dry laboratory. Observed thresholds varied as a function of stimulus type and spectral content. Thresholds for band-limited noises were unaffected by center frequency and equal to that of white noise. For HS, however, thresholds decreased as the fundamental frequency of the stimulus increased. The third experiment was a replication of the second in a reverberant concert hall, which produced qualitatively similar results except that thresholds were significantly higher than in the acoustically dry laboratory.

Visual recalibration of auditory spatial perception: two separate neural circuits for perceptual learning.

A remarkable example of rapid perceptual learning is the visual recalibration of auditory spatial perception, which can result in either a bias (ventriloquism after-effect) or an improvement (multisensory enhancement) in auditory localization. Here, we examine the possibility that these after-effects might depend on two distinct neural pathways (geniculostriate vs. collicular-extrastriate). To this end, patients with a lesion of the striate cortex (hemianopic patients) or temporoparietal cortex (neglect patients) were asked to localize weak sounds, before and after a brief exposure to repetitive auditory-visual stimulation which was given either in the normal or in the affected field. Adaptation comprised spatially disparate (Experiment 1) or spatially coincident (Experiment 2) auditory-visual stimuli. After exposure to spatially disparate stimuli in the normal field, all patients exhibited the usual shifts toward the visual attractor, at each sound location. In contrast, when the same kind of adaptation was given in the affected field, a consistent shift was still evident in neglect patients but not in patients with hemianopia. After adaptation to spatially coincident stimuli, and regardless of the adaptation hemifield, all patients exhibited a significant improvement in auditory localization, which was largest for sounds presented at the adapted location. The findings suggest the presence of two distinct recalibration mechanisms. Adapting to spatially conflicting stimuli invokes a corrective mechanism implemented within the geniculostriate circuit, which tries to reduce the registered discrepancy. Adapting to spatially aligned inputs invokes a mechanism implemented along a collicular-extrastriate circuit, which tries to reduce the localization error.

Walking along curved paths of different angles: the relationship between head and trunk turning.

Walking along a curved path requires coordinated motor actions of the entire body. Here, we investigate the relationship between head and trunk movements during walking. Previous studies have found that the head systematically turns into turns before the trunk does. This has been found to occur at a constant distance rather than at a constant time before a turn. We tested whether this anticipatory head behavior is spatially invariant for turns of different angles. Head and trunk positions and orientations were measured while participants walked around obstacles in 45 degrees, 90 degrees, 135 degrees or 180 degrees turns. The radius of the turns was either imposed or left free. We found that the head started to turn into the direction of the turn at a constant distance before the obstacle (approximately 1.1 m) for turn angles up to 135 degrees . During turns, the head was consistently oriented more into the direction of the turn than the trunk. This difference increased for larger turning angles and reached its maximum later in the turn for larger turns. Walking speeds decreased monotonically for increasing turn angles. Imposing fixed turn radii only affected the point at which the trunk started to turn into a turn. Our results support the view that anticipatory head movements during turns occur in order to gather advance visual information about the trajectory and potential obstacles.

The aftereffects of ventriloquism: generalization across sound-frequencies.

Exposure to synchronous but spatially discordant auditory and visual inputs produces, beyond immediate cross-modal biases, adaptive recalibrations of the respective localization processes that manifest themselves in aftereffects. Such recalibrations probably play an important role in maintaining the coherence of spatial representations across the various spatial senses. The present study is part of a research program focused on the way recalibrations generalize to stimulus values different from those used for adaptation. Considering the case of sound frequency, we recently found that, in contradiction with an earlier report, auditory aftereffects generalize nearly entirely across two octaves. In this new experiment, participants were adapted to an 18 degrees auditory-visual discordance with either 400 or 6400 Hz tones, and their subsequent sound localization was tested across this whole four-octave frequency range. Substantial aftereffects, decreasing significantly with increasing difference between test and adapter frequency, were obtained at all combinations of adapter and test frequency. Implications of these results concerning the functional site at which visual recalibration of auditory localization might take place are discussed.

The aftereffects of ventriloquism: are they sound-frequency specific?

Exposing different sense modalities (like sight, hearing or touch) to repeated simultaneous but spatially discordant stimulations generally causes recalibration of localization processes in one or both of the involved modalities, which is manifested through aftereffects. These provide opportunities for determining the extent of the changes induced by the exposure. Taking the so-called ventriloquism situation, in which synchronized sounds and light flashes are delivered in different locations, we examine if auditory recalibration produced by exposing tones of one frequency to attraction by discordant light flashes generalizes to different frequencies. Contrary to an earlier report, generalization was obtained across two octaves. This result did not depend on which modality attention was forced on through catch trials during exposure. Implications concerning the functional site of recalibration are briefly discussed.

The effect of visual degradation on anticipatory and compensatory steering control.

It has long been held that steering a vehicle is subserved by two distinct visual processes, a compensatory one for maintaining lane position and an anticipatory one for previewing the curvature of the upcoming road. In this study, we investigated the robustness of these two steering control processes by systematically degrading their visual inputs. Performance was measured at the level of vehicle position and at the level of the actions on the steering wheel. The results show that the compensatory process is more robust to visual degradation than the anticipatory process. The results are also consistent with the idea that steering is under the supervision of a combination of compensatory and anticipatory mechanisms, although they suggest that the quality of the sensory information will determine how information is combined.

Auditory velocity discrimination in the horizontal plane at very high velocities.

We determined velocity discrimination thresholds and Weber fractions for sounds revolving around the listener at very high velocities. Sounds used were a broadband white noise and two harmonic sounds with fundamental frequencies of 330 Hz and 1760 Hz. Experiment 1 used velocities ranging between 288°/s and 720°/s in an acoustically treated room and Experiment 2 used velocities between 288°/s and 576°/s in a highly reverberant hall. A third experiment addressed potential confounds in the first two experiments. The results show that people can reliably discriminate velocity at very high velocities and that both thresholds and Weber fractions decrease as velocity increases. These results violate Weber's law but are consistent with the empirical trend observed in the literature. While thresholds for the noise and 330 Hz harmonic stimulus were similar, those for the 1760 Hz harmonic stimulus were substantially higher. There were no reliable differences in velocity discrimination between the two acoustical environments, suggesting that auditory motion perception at high velocities is robust against the effects of reverberation.

The aftereffects of ventriloquism: the time course of the visual recalibration of auditory localization.

Exposure to synchronous but spatially discordant auditory and visual inputs produces adaptive recalibration of the respective localization processes, which manifest themselves in measurable aftereffects. Here we report two experiments that examined the time course of visual recalibration of apparent sound location in order to establish the build-up and dissipation of recalibration. In Experiment 1 participants performed a sound localization task before and during exposure to an auditory-visual discrepancy. In Experiment 2, participants performed a sound localization task before and after 60, 180 or 300 exposures to the discrepancy and aftereffects were measured across a series of post-adaptation sound localization trials. The results show that recalibration is very fast. Substantial aftereffects are obtained after only 18-24 exposures and asymptote appears to be reached between 60 and 180 exposures. The rate of adaptation was independent of the size of the discrepancy. The retention of the aftereffect was strong, as we found no dissipation, not even after as few as 60 exposure trials.

The effects of voluntary movements on auditory-haptic and haptic-haptic temporal order judgments.

In two experiments we investigated the effects of voluntary movements on temporal haptic perception. Measures of sensitivity (JND) and temporal alignment (PSS) were obtained from temporal order judgments made on intermodal auditory-haptic (Experiment 1) or intramodal haptic (Experiment 2) stimulus pairs under three movement conditions. In the baseline, static condition, the arm of the participants remained stationary. In the passive condition, the arm was displaced by a servo-controlled motorized device. In the active condition, the participants moved voluntarily. The auditory stimulus was a short, 500Hz tone presented over headphones and the haptic stimulus was a brief suprathreshold force pulse applied to the tip of the index finger orthogonally to the finger movement. Active movement did not significantly affect discrimination sensitivity on the auditory-haptic stimulus pairs, whereas it significantly improved sensitivity in the case of the haptic stimulus pair, demonstrating a key role for motor command information in temporal sensitivity in the haptic system. Points of subjective simultaneity were by-and-large coincident with physical simultaneity, with one striking exception in the passive condition with the auditory-haptic stimulus pair. In the latter case, the haptic stimulus had to be presented 45ms before the auditory stimulus in order to obtain subjective simultaneity. A model is proposed to explain the discrimination performance.

Walking straight into circles.

Common belief has it that people who get lost in unfamiliar terrain often end up walking in circles. Although uncorroborated by empirical data, this belief has widely permeated popular culture. Here, we tested the ability of humans to walk on a straight course through unfamiliar terrain in two different environments: a large forest area and the Sahara desert. Walking trajectories of several hours were captured via global positioning system, showing that participants repeatedly walked in circles when they could not see the sun. Conversely, when the sun was visible, participants sometimes veered from a straight course but did not walk in circles. We tested various explanations for this walking behavior by assessing the ability of people to maintain a fixed course while blindfolded. Under these conditions, participants walked in often surprisingly small circles (diameter < 20 m), though rarely in a systematic direction. These results rule out a general explanation in terms of biomechanical asymmetries or other general biases [1-6]. Instead, they suggest that veering from a straight course is the result of accumulating noise in the sensorimotor system, which, without an external directional reference to recalibrate the subjective straight ahead, may cause people to walk in circles.

The aftereffects of ventriloquism: patterns of spatial generalization.

We examined how visual recalibration of apparent sound location obtained at a particular location generalizes to untrained locations. Participants pointed toward the origin of tone bursts scattered along the azimuth, before and after repeated exposure to bursts in one particular location, synchronized with point flashes of light a constant distance to their left/right. Adapter tones were presented straight ahead in Experiment 1, and in the left or right periphery in Experiment 2. With both arrangements, different generalization patterns were obtained on the visual distractor's side of the auditory adapter and onthe opposite side. On the distractor side, recalibration generalized following a descending gradient; practically no generalization was observed on the other side. This dependence of generalization patterns on the direction of the discordance imposed during adaptation has not been reported before, perhaps because the experimental designs in use did not allow its observation.

A modulatory role for facial expressions in prosopagnosia.

Brain-damaged patients experience difficulties in recognizing a face (prosopagnosics), but they can still recognize its expression. The dissociation between these two face-related skills has served as a keystone of models of face processing. We now report that the presence of a facial expression can influence face identification. For normal viewers, the presence of a facial expression influences performance negatively, whereas for prosopagnosic patients, it improves performance dramatically. Accordingly, although prosopagnosic patients show a failure to process the facial configuration in the interest of face identification, that ability returns when the face shows an emotional expression. Accompanying brain-imaging results indicate activation in brain areas (amygdala, superior temporal sulcus, parietal cortex) outside the occipitotemporal areas normally activated for face identification and lesioned in these patients. This finding suggests a modulatory role of these areas in face identification that is independent of occipitotemporal face areas.