Visual cues and perceived reachability

A rather consistent finding in studies of perceived (imagined) compared to actual movement in a reaching paradigm is the tendency to overestimate at midline. Explanations of such behavior have focused primarily on perceptions of postural constraints and the notion that individuals calibrate reachability in reference to multiple degrees of freedom, also known as the whole-body explanation. The present study examined the role of visual information in the form of binocular and monocular cues in perceived reachability. Right-handed participants judged the reachability of visual targets at midline with both eyes open, dominant eye occluded, and the non-dominant eye covered. Results indicated that participants were relatively accurate with condition responses not being significantly different in regard to total error. Analysis of the direction of error (mean bias) revealed effective accuracy across conditions with only a marginal distinction between monocular and binocular conditions. Therefore, within the task conditions of this experiment, it appears that binocular and monocular cues provide sufficient visual information for effective judgments of perceived reach at midline.     

Maturational and situational determinants of reaching at its onset

At 3 months of age, reaching behavior was measured in a group of 10 girls and 10 boys born at term. The assessments were carried out on the average 2 days after reaching onset. Reaching kinematics was measured in both supine and reclined positions. Girls reached more than boys, had straighter reaching trajectories and movements of shorter durations as well as fewer movement units. The reclined position gave rise to straighter trajectories in both girls and boys. Several anthropometric parameters were measured. Girls had less length and volume of the forearm than boys but similar upper arm volumes. There was a weak relation between kinematic and anthropometric variables.     

Numeric comparison in a visually-guided manual reaching task

Nearly all studies on perception and cognition have used discrete responses to infer internal cognitive processes. In the current study, we demonstrate that visually-guided manual reaching can provide new opportunities to access internal processes over time. In each trial, participants were required to compare a single digit Arabic number presented on the center square with the standard, 5. Participants were asked to reach and touch one of three squares on the screen with their index finger while their hand movement trajectories were recorded: the left square for 1-4, the center for 5, and the right for 6-9. Direct evidence for an analogue representation of numbers was found in early as well as in later portions of hand trajectories, showing systematic shifts in position for small differences in numerical magnitude.     

Multisensory spatial representations in eye-centered coordinates for reaching

Humans can reach for objects with their hands whether the objects are seen, heard or touched. Thus, the position of objects is recoded in a joint-centered frame of reference regardless of the sensory modality involved. Our study indicates that this frame of reference is not the only one shared across sensory modalities. The location of reaching targets is also encoded in eye-centered coordinates, whether the targets are visual, auditory, proprioceptive or imaginary. Furthermore, the remembered eye-centered location is updated after each eye and head movement. This is quite surprising since, in principle, a reaching motor command can be computed from any non-visual modality without ever recovering the eye-centered location of the stimulus. This finding may reflect the predominant role of vision in human spatial perception.     

The development of reaching behavior in low-risk preterm infants

This longitudinal study investigated the development of reaching behavior in the seated position in preterm infants at the ages of 5–7 months by analyzing kinematic variables (straightness and adjustment indexes, movement unit, mean and final velocities). The correlation between kinematic variables and grasping was verified. The participants were nine low-risk preterm infants with no cerebral lesions. Ten fullterm infants served as control. In both groups, kinematic variables remained unchanged over age, except for the adjustment index, which was higher at 6 months in the preterm group. Successful grasping increased in both groups over age and it was shown to be negatively correlated with mean velocity in the preterm infants. At the ages of 6 and 7 months, preterms showed lower mean and final velocities and higher adjustment index when compared with fullterms. The relative constancy in the kinematic variables suggests that, after having explored the action possibilities during the acquisition phase, the infants selected an adaptative pattern to perform the reaching movements. Slower movements and greater adjustments may be functional strategies of preterms to achieve successful grasps.     

Suprasegmental lexical stress cues in visual speech can guide spoken-word recognition

Visual cues to the individual segments of speech and to sentence prosody guide speech recognition. The present study tested whether visual suprasegmental cues to the stress patterns of words can also constrain recognition. Dutch listeners use acoustic suprasegmental cues to lexical stress (changes in duration, amplitude, and pitch) in spoken-word recognition. We asked here whether they can also use visual suprasegmental cues. In two categorization experiments, Dutch participants saw a speaker say fragments of word pairs that were segmentally identical but differed in their stress realization (e.g., ?ca-vi from cavia “guinea pig” vs. ?ka-vi from kaviaar “caviar”). Participants were able to distinguish between these pairs from seeing a speaker alone. Only the presence of primary stress in the fragment, not its absence, was informative. Participants were able to distinguish visually primary from secondary stress on first syllables, but only when the fragment-bearing target word carried phrase-level emphasis. Furthermore, participants distinguished fragments with primary stress on their second syllable from those with secondary stress on their first syllable (e.g., pro-?jec from projector “projector” vs. ?pro-jec from projectiel “projectile”), independently of phrase-level emphasis. Seeing a speaker thus contributes to spoken-word recognition by providing suprasegmental information about the presence of primary lexical stress.     

Selective scanpath repetition during memory-guided visual search

Visual search efficiency improves with repetition of a search display, yet the mechanisms behind these processing gains remain unclear. According to Scanpath Theory, memory retrieval is mediated by repetition of the pattern of eye movements or “scanpath” elicited during stimulus encoding. Using this framework, we tested the prediction that scanpath recapitulation reflects relational memory guidance during repeated search events. Younger and older subjects were instructed to find changing targets within flickering naturalistic scenes. Search efficiency (search time, number of fixations, fixation duration) and scanpath similarity (repetition) were compared across age groups for novel (V1) and repeated (V2) search events. Younger adults outperformed older adults on all efficiency measures at both V1 and V2, while the search time benefit for repeated viewing (V1–V2) did not differ by age. Fixation-binned scanpath similarity analyses revealed repetition of initial and final (but not middle) V1 fixations at V2, with older adults repeating more initial V1 fixations than young adults. In young adults only, early scanpath similarity correlated negatively with search time at test, indicating increased efficiency, whereas the similarity of V2 fixations to middle V1 fixations predicted poor search performance. We conclude that scanpath compression mediates increased search efficiency by selectively recapitulating encoding fixations that provide goal-relevant input. Extending Scanpath Theory, results suggest that scanpath repetition varies as a function of time and memory integrity.     

Separating value from selection frequency in rapid reaching biases to visual targets

Stimuli associated with positive rewards in one task often receive preferential processing in a subsequent task, even when those associations are no longer relevant. Here we use a rapid reaching task to investigate these biases. In Experiment 1 we first replicated the learning procedure of Raymond and O'Brien (2009), for a set of arbitrary shapes that varied in value (positive, negative) and probability (20%, 80%). In a subsequent task, participants rapidly reached toward one of two shapes, except now the previously learned associations were irrelevant. As in the previous studies, we found significant reach biases toward shapes previously associated with a high probable, positive outcome. Unexpectedly, we also found a bias toward shapes previously associated with a low probable, negative outcome. Closer inspection of the learning task revealed a potential second factor that might account for these results; since a low probable negative shape was always paired with a high probable negative shape, it was selected with disproportionate frequency. To assess how selection frequency and reward value might both contribute to reaching biases we performed a second experiment. The results of this experiment at a group level replicated the reach-bias toward positively rewarding stimuli, but also revealed a separate bias toward stimuli that had been more frequently selected. At the level of individual participants, we observed a variety of preference profiles, with some participants biased primarily by reward value, others by frequency, and a few actually biased away from both highly rewarding and high frequency targets. These findings highlight that: (1) rapid reaching provides a sensitive readout of preferential processing; (2) target reward value and target selection frequency are separate sources of bias; and (3) group-level analyses in complex decision-making tasks can obscure important and varied individual differences in preference profiles.     

Development of infant reaching behaviors: Kinematic changes in touching and hitting

This longitudinal study investigated the development of reaching in typical infants, from age 4 to 8 months, and described the pattern of hand kinematics underlying changes in the characteristics of infants’ actions while reaching for a target. Thirteen infants were followed biweekly. Two reaching behaviors emerged during the infants’ free interactions with the target, touching and hitting. Changes over time were documented for the number of movement units, straightness index, distance, peak velocity and time to peak velocity of the hand for touches and hits. We observed increases in the numbers of touches and hits and changes in hand kinematics over time; the distance traveled by the hand was greater for hitting compared to touching. These kinematic changes were specific to the movement patterns that infants adopted to reach to the target.     

Mountain high,valley low: Direction-specific effects of articulation on reaching

Representations underpinning action and language overlap and interact very closely. There are bidirectional interactions between word and action comprehension, semantic processing of language, and response selection. This study extends our understanding of the influence of speech on concurrent motor execution. Participants reached-to-grasp the top or bottom of a vertically oriented bar in response to the location of a word on a computer screen (top/bottom). Words were synonyms for “up” or “down”, and participants were required to articulate the word during movement. We were particularly interested in the influence of articulated word semantics on the transport component of the reach. Using motion capture to analyse action kinematics, we show that irrespective of reach direction, saying “up” synonyms led to greater height of the hand, while saying “down” synonyms was associated with reduced height. This direction-specific influence of articulation on the spatial parameters of the hand supports the idea that linguistic systems are tightly integrated and influence each other.     

A study of reaching actions in walking infants

Acquiring motor skills transforms the perceptual and cognitive world of infants and expands their exploratory engagement with objects. This study investigated how reaching is integrated with walking among infant walkers (n = 23, 14.5–15.5 months). In a walk-to-reach paradigm, diverse object retrieval strategies were observed. All infants were willing to use their upper and lower bodies in concert, and the timing of this coordination reflected features of their environment. Infants with an older walking age (months since walking onset) retrieved items more rapidly and exploited their non-reaching hand more effectively during object retrieval than did same-age infants with a younger walking age. This suggests that the actions of the upper- and lower-body are flexibly integrated and that this integration may change across development. Mechanisms that shape sophisticated upper-body use during upright object retrieval are discussed. Infants flexibly integrate emerging motor skills in the service of object retrieval in ways not previously documented.     

Using spatial vibrotactile cues to direct visual attention in driving scenes

We report two experiments designed to investigate the potential use of vibrotactile warning signals to present spatial information to car drivers. Participants performed an attention-demanding rapid serial visual presentation (RSVP) monitoring task. Meanwhile, whenever they felt a vibrotactile stimulus presented on either their front or back, they had to check the front and the rearview mirror for the rapid approach of a car, and brake or accelerate accordingly. We investigated whether speeded responses to potential emergency driving situations could be facilitated by the presentation of spatially-predictive (80% valid; Experiment 1) or spatially-nonpredictive (50% valid; Experiment 2) vibrotactile cues. Participants responded significantly more rapidly following both spatially-predictive and spatially-nonpredictive vibrotactile cues from the same rather than the opposite direction as the critical driving events. These results highlight the potential utility of vibrotactile warning signals in automobile interface design for directing a driver’s visual attention to time-critical events or information.     

No evidence for accurate visuomotor memory: systematic and variable error in memory-guided reaching

The authors explored whether the motor system has access to highly accurate information about the aiming environment after visual occlusion. Participants (N = 14) reached to 1 of 3 midsagittal targets in 4 visual conditions (open-loop, brief-delay, 500-ms delay, and 2,000-ms delay). In all conditions, the aiming environment was first viewed for 2,000 ms. Movements were cued immediately after the initial viewing period in the open-loop and brief-delay conditions. Vision was not occluded until movement onset in the open-loop condition, whereas vision was occluded coincidentally with the movement cue in the brief-delay condition. In the 2 longer delay conditions, the movement was cued following a 500- or a 2,000-ms no-vision delay period. Participants overshot the target in the open-loop condition, but that tendency was significantly reduced in the 3 delay conditions. Moreover, endpoint variability was greater in the 3 delay conditions than in the open-loop condition. A speed-accuracy tradeoff account could not explain the differences between open-loop and delayed reaching. Those findings suggest that the motor system does not have access to highly accurate information about the aiming environment for any appreciable period of time following visual occlusion, consistent with the view that the visuomotor system operates in real time.     

How to (and how not to) think about top-down influences on visual perception

The question of whether cognition can influence perception has a long history in neuroscience and philosophy. Here, we outline a novel approach to this issue, arguing that it should be viewed within the framework of top-down information-processing. This approach leads to a reversal of the standard explanatory order of the cognitive penetration debate: we suggest studying top-down processing at various levels without preconceptions of perception or cognition. Once a clear picture has emerged about which processes have influences on those at lower levels, we can re-address the extent to which they should be considered perceptual or cognitive. Using top-down processing within the visual system as a model for higher-level influences, we argue that the current evidence indicates clear constraints on top-down influences at all stages of information processing; it does, however, not support the notion of a boundary between specific types of information-processing as proposed by the cognitive impenetrability hypothesis.     

Contingent auditory feedback of arm movement facilitates reaching behavior in infancy

The purpose of this study was to investigate the influence of contingent auditory feedback on the development of infant reaching. Eleven full-term infants were observed biweekly from the age of 10 weeks to 16 weeks, and their arm kinematics were recorded. Auditory feedback that was contingent on arm kinematics was provided in the form of: (a) the mother's voice; and (b) musical tones. Results showed that providing auditory feedback (mother's voice or musical tones): (i) increased the amplitude of exploratory arm movements before the onset of reaching; and (ii) increased the number of reaches at the onset of reaching. These results show that infants are able to use contingent auditory feedback to explore the relevant possibilities for action that are subsequently shaped into goal-directed movements.     

Effects of background color on detecting spot stimuli in the upper and lower visual fields

Participants were required to detect spot stimuli briefly presented to the upper, central, or lower visual fields. The stimuli were presented either on a green or a red background. Results showed that reaction time (RT) was shorter for the lower visual field (LVF) compared to the upper visual field (UVF). Furthermore, this LVF advantage was significantly reduced in the red background condition compared to the green one. A red light is known to suppress activity of the magno-dominated stream. Therefore, the LVF advantage in RT can be explained as resulting from the biased representation of the magno-dominated stream in the LVF.     

Toy-oriented changes in hand and joint kinematics during the emergence of purposeful reaching

Infants first consistently reach for objects between 3 and 5 months of age. In the months before reaching, infants produce a variety of arm movements. The relationship between these early arm movements and the emergence of purposeful reaching is still unclear. The purpose of the present study was to determine how groups of non-reaching, nearly reaching, and newly reaching infants changed the kinematics of their spontaneous arm movements in the presence of a toy. Five infants in each of these groups were observed with a high-speed motion capture system during trials with and without a toy present. Kinematic analyses examined 3D hand, shoulder, and elbow motions. Our results suggest that with a toy present, non-reachers altered their movement quantity whereas near- and new-reachers altered their movement quality through spatio-temporal dissociation and reorientation of the arm. When comparing the changes across groups we observed three preliminary patterns of toy-oriented changes. Our results join other studies to strengthen the relationship between early arm movements and purposeful reaching. Future longitudinal studies are now required to begin to fully understand the complex process by which infants adapt their early arm movements for purposeful behaviors.     

Sub-threshold cuing: Saccadic responses to low-contrast,peripheral, transient visual landmark cues

Dorsal stream visual encoding was studied in three experiments, by examining effects of peripheral landmark cues on eye movements. Stimulus features and task structure were tailored to physiological and functional characterisations of the dorsal visual stream. Sub-discriminable peripheral stimuli served as landmark cue stimuli. In Experiments 1 and 2, orienting behaviour in response to cues and targets differed for participants with relatively low and relatively high peripheral contrast thresholds. In Experiment 1, low, but not high-threshold participants oriented towards landmark cues that could not be discriminated consciously. However, in Experiment 3, high-, but not low-threshold participants oriented towards near threshold cues. Hence, under appropriate conditions both groups of participants oriented in response to brief, low-contrast, peripheral information. We propose that landmark cueing may provide a useful tool for measuring individual differences in dorsal stream processing and dynamic aspects of visual functioning and awareness.     

New insights on eye blindness and hand sight: Temporal constraints of visuo-motor networks

Pioneer experiments on saccadic suppression have shown that this effect is not followed by motor disorientation: Conscious perception of a target displacement can be dissociated from correct manual target reaching. It has subsequently been demonstrated that movement corrections with the same latency and spatial characteristics can be produced in conditions allowing perceptual awareness of perturbation of a target as in condition inducing saccadic suppression. In addition to the qualitative dissociation between motor performance and conscious awareness, quantitative temporal dissociations in action can be observed by manipulating different features of the visual target. When the target of an ongoing simple action is perturbed, a temporal advantage is found for responses to perturbations of location relative to colour and shape. Furthermore, there seems to be a temporal advantage for automatic motor corrections made in response to a target displacement as compared to other responses (other ongoing movement adjustments, movement interruption, conditional motor response such as pressing a key, verbal response, delayed matching-to-sample tasks). Thus, this paper reviews evidence for the fact that the temporal characteristics of any given response to a stimulus are dependent both on the sensory processes and on the type of response generated. Accordingly, identification responses (such as verbal report) to a visual stimulus are much slower than motor corrections of an ongoing movement in response to a target location change because of different processing times of the stimulus features (“What” compared to “Where”) and of the response itself (“What” compared to “How”). The existence of two continua (What/Where and What/How) is proposed between these two extreme stimulus- response combinations. This model may be a useful framework to better understand visuo-motor transformations and the network of connections between visual and motor areas.