The Complexity of Head Movement is Correlated with Learning about Affordances for Walking.

We asked whether the quantitative kinematics of standing postural activity might be related to short-term learning of affordances. Standing participants viewed a narrow path for 15 s, and then gave perceptual reports about the distance that they could walk along the path while wearing a weighted vest (novel affordance) or while not wearing the vest (familiar affordance). In a control condition, participants gave perceptual reports about egocentric distance along the path. During the 15 s viewing intervals, we measured the kinematics of head and torso movement as standing participants made a series of 12 perceptual reports. Perceptual reports improved across trials, but only in the condition in which participants were asked to perceive a novel affordance. The dynamical complexity of head movement changed across trials as participants gave perceptual reports about the novel affordance, but did not change systematically when perceiving a familiar affordance, or a non-affordance egocentric distance. We argue that the dynamical complexity of postural activity may have served an exploratory function supporting the learning of a novel affordance. Our results are consistent with the broader hypothesis that affordances are learned through active engagement with the environment, rather than (for example) through abstract cognitive processing.

The Affordance Directive: Affordance Priming Facilitates Object Detection Similar to Semantic Priming.

The present study investigated differences in priming perceptions of target objects via affordance or semantic primes. Affordances denote possibilities for action in relation to objects (e.g., chair - sit), whereas semantic primes describe related concepts and features of objects (e.g., chair - legs). In Experiments 1A/1B the effects of affordance and semantic priming were compared via a semantic-categorization task using a normed word list of objects. In Experiments 2-4 we investigated affordance priming on object identification of pictures using a shoebox-classification task. In Experiment 1A participants were asked to respond by categorizing the presented word as concrete or abstract. Experiment 1B was similar to 1A, but with a 1000 ms response deadline. Experiment 2 presented target objects as words or photographs. Experiment 3 presented target objects as photographs degraded at three levels (clear, medium blur, extreme blur). Experiment 4 presented target objects as photographs that began degraded and slowly became clear. Experiment 1B found word priming for semantic primes, but not affordances. In contrast, Experiments 2-4 found object priming was facilitated by both affordances and semantic primes. Collectively, our results indicate that affordances facilitate object classification.

Does optic flow provide information about actions?

Optic flow, the pattern of light generated in the visual field by motion of objects and the observer's body, serves as information that underwrites perception of events, actions, and affordances. This visual pattern informs the observer about their own actions in relation to their surroundings, as well as those of others. This study explored the limits of action detection for others as well as the role of optic flow. First-person videos were created using camera recordings of the actor's perspective as they performed various movements (jumping jacks, jumping, squatting, sitting, etc.). In three experiments participants attempted to detect the action from first-person video footage using open ended responses (Experiment 1), forced-choice responses (Experiment 2), and a match-to-sample paradigm (Experiment 3). It was discovered that some actions are more difficult to detect than others. When the task was challenging (Experiment 1) athletes were more accurate, but this was not the case in Experiments 2 and 3. All actions were identified above chance level across viewpoints, suggesting that invariant information was detected and used to perform the task.

How frequent is the spontaneous occurrence of synchronized walking in daily life?

Experimental work has suggested that individuals walking side by side may frequently synchronize their steps. The present study created video records of pedestrian activity on pedestrian pathways in order to estimate the frequency of continuous synchronization among pairs of walkers going about their daily lives. About 6% of 498 coded pairs were continuously synchronized. Analysis and modeling of the distributions of frequency differences suggested that while different walkers will tend to have different preferred frequencies for a given speed (i.e., a preferred ratio of step length to step frequency, or walk ratio), they may tend to adjust their walk ratios slightly toward one another's even when they are not synchronizing their steps.

Functional Specificity of the Affordance of Reaching.

The information that specifies whether an object is within reach is a complex pattern that depends on body-scaled parameters measured from an egocentric reference point. The pattern is a function of relevant body proportions (eye height, shoulder height [SH], arm length) with respect to the spatial location of the target object. In addition to not knowing how these factors map onto perception, it is also not known whether the egocentric viewpoint is centered at the eye or the shoulder. In three experiments, we systematically tested whether observers can perceive eye height and SH (Experiment 1), whether they can point accurately in the direction of a target object (Experiment 2), and whether they can point accurately to judge if the target object is within reach (Experiment 3). Experiment 1 demonstrated that participants are more accurate at judging their own eye height than SH. Experiment 2 revealed that participants can more accurately point to a target object's location when measured from the shoulder as a reference point than when measured from the eye. In Experiment 3, we showed that a higher-order variable that includes arm length, body height, and angle of declination to the target successfully predicted affordance judgments, regardless of a reference point. We consider this as evidence that the invariant is functionally specific, not tied to any one particular anatomical body part.

Visual and Haptic Perception of Affordances of Feelies.

Most objects have well-defined affordances. Investigating perception of affordances of objects that were not created for a specific purpose would provide insight into how affordances are perceived. In addition, comparison of perception of affordances for such objects across different exploratory modalities (visual vs. haptic) would offer a strong test of the lawfulness of information about affordances (i.e., the invariance of such information over transformation). Along these lines, "feelies"- objects created by Gibson with no obvious function and unlike any common object-could shed light on the processes underlying affordance perception. This study showed that when observers reported potential uses for feelies, modality significantly influenced what kind of affordances were perceived. Specifically, visual exploration resulted in more noun labels (e.g., "toy") than haptic exploration which resulted in more verb labels (i.e., "throw"). These results suggested that overlapping, but distinct classes of action possibilities are perceivable using vision and haptics. Semantic network analyses revealed that visual exploration resulted in object-oriented responses focused on object identification, whereas haptic exploration resulted in action-oriented responses. Cluster analyses confirmed these results. Affordance labels produced in the visual condition were more consistent, used fewer descriptors, were less diverse, but more novel than in the haptic condition.

Complexity of postural sway affects affordance perception of reachability in virtual reality.

Visual perception of whether an object is within reach while standing in different postures was investigated. Participants viewed a three-dimensional (3D) virtual reality (VR) environment with a stimulus object (red ball) placed at different egocentric distances. Participants reported whether the object was reachable while in a standard pose as well as in two separate active balance poses (yoga tree pose and toe-to-heel pose). Feedback on accuracy was not provided, and participants were not allowed to attempt to reach. Response time, affordance judgements (reachable and not reachable), and head movements were recorded on each trial. Consistent with recent research on perception of reaching ability, the perceived boundary occurred at approximately 120% of arm length, indicating overestimation of perceived reaching ability. Response times increased with distance, and were shortest for the most difficult pose-the yoga tree pose. Head movement amplitude increased with increases in balance demands. Unexpectedly, the coefficient of variation was comparable in the two active balance poses, and was more extreme in the standard control pose for the shortest and longest distances. More complex descriptors of postural sway (i.e., effort-to-compress) were predictive of perception while in the tree pose and the toe-to-heel pose, as compared with control stance. This demonstrates that standard measures of central tendency are not sufficient for describing multiscale interactions of postural dynamics in functional tasks.

Comparison of two psychophysical methods across visual and haptic perception of stand-on-ability.

Recent research (Hajnal et al. in Perception 45(7):768-786, 2016) found apparent differences between haptic and visual perception of the affordance of stand-on-ability. One reason for this discrepancy might be the imprecision of the measurement method. We compared the psychophysical method of adjustment with a dynamic staircase method of stimulus presentation in an affordance task. Three groups of participants either visually inspected a flat sturdy sloped ramp, placed one foot onto the ramp occluded from view, or placed one foot on the ramp while allowed to look at it, in the visual, haptic, or multimodal condition, respectively. Each trial was presented by moving the ramp up or down until the participant perceived the action boundary, i.e., the steepest slope that still afforded upright stance. After perceptual trials, we measured the actual action boundaries by allowing participants to attempt to stand on the ramp. The action boundary was the average between the lowest false alarm and steepest hit within a 1.5° margin of difference. Visual perception was found to be equivalent with haptic perception. Perceptual and action boundaries were indistinguishable, but only when employing the more precise staircase method. The results support the postulate of equivalence among perceptual systems proposed by Gibson (The senses considered as perceptual systems. Houghton Mifflin Company, Boston, 1966), and the idea of correspondence between perception and action which is the cornerstone of affordance theory.

Multifractality of posture modulates multisensory perception of stand-on-ability.

By definition, perception is a multisensory process that unfolds in time as a complex sequence of exploratory activities of the organism. In such a system perception and action are integrated, and multiple energy arrays are available simultaneously. Perception of affordances interweaves sensory and motor activities into meaningful behavior given task constraints. The present contribution offers insight into the manner in which perception and action usher the organism through competent functional apprehension of its surroundings. We propose that the tensegrity structure of the body, manifested via multifractality of exploratory bodily movements informs perception of affordances. The affordance of stand-on-ability of ground surfaces served as the experimental paradigm. Observers viewed a surface set to a discrete angle and attempted to match it haptically with a continuously adjustable surface occluded by a curtain, or felt an occluded surface set to a discrete angle then matched it visually with a continuously adjustable visible surface. The complex intertwining of perception and action was demonstrated by the interactions of multifractality of postural sway with multiple energy arrays, responses, and changing geometric task demands.

Fractality of body movements predicts perception of affordances: Evidence from stand-on-ability judgments about slopes.

We recorded head motion with one wireless marker attached to the back of the head during quiet stance as participants visually inspected a sloped ramp in order to perceive whether they might be able to stand on the surface. Participants responded with "yes" or "no" without attempting to stand on the ramp. As has been found in dynamic touch (Palatinus, Kelty-Stephen, Kinsella-Shaw, Carello, & Turvey, 2014), we hypothesized that multiscale fluctuation patterns in bodily movement during visual observation would predict perceptual judgments. Mixed-effects logistic regression predicted binary affordance judgments as a function of geographical slant angle, head-motion standard deviation, and multifractal spectrum width (Ihlen, 2012). Multifractal spectrum width was the strongest predictor of affordance judgments. Specifically, increased spectrum width predicted decreased odds of a "yes" answer. Interestingly, standard deviation was not a significant predictor, reinforcing our prediction that traditional measures of variability fail to account for what fractal measures of multiscale interactions can predict about information pickup in perception-action systems. (PsycINFO Database Record

Heads Up!

Possibilities for behavior (i.e., affordances) can be perceived with units spanning anatomical components and external objects. For example, affordances for standing on an inclined surface can be perceived with an object held in the hand or attached to the head. We investigated whether these two person-plus-object perceptual systems exhibit the same pattern of nonlinear phase transitions in perception of this affordance. Blindfolded participants explored an inclined surface with a rod held in the hand or attached to the head and reported whether they could stand on that surface. Inclinations were presented in ascending or descending sequences. In both conditions, responses exhibited negative hysteresis - perceptual boundaries occurred at steeper angles for descending than for ascending sequences. The generalization of this pattern across components that differ in physiology, sensitivity, and experience is consistent with both the soft assembly of perceptual devices and with a dynamical systems perspective on perception of affordances.

Perception of Stand-on-ability: Do Geographical Slants Feel Steeper Than They Look?

Past research has shown that haptically perceived surface slant by foot is matched with visually perceived slant by a factor of 0.81. Slopes perceived visually appear shallower than when stood on without looking. We sought to identify the sources of this discrepancy by asking participants to judge whether they would be able to stand on an inclined ramp. In the first experiment, visual perception was compared to pedal perception in which participants took half a step with one foot onto an occluded ramp. Visual perception closely matched the actual maximal slope angle that one could stand on, whereas pedal perception underestimated it. Participants may have been less stable in the pedal condition while taking half a step onto the ramp. We controlled for this by having participants hold onto a sturdy tripod in the pedal condition (Experiment 2). This did not eliminate the difference between visual and haptic perception, but repeating the task while sitting on a chair did (Experiment 3). Beyond balance requirements, pedal perception may also be constrained by the limited range of motion at the ankle and knee joints while standing. Indeed, when we restricted range of motion by wearing an ankle brace pedal perception underestimated the affordance (Experiment 4). Implications for ecological theory were offered by discussing the notion of functional equivalence and the role of exploration in perception.

Use your head! Perception of action possibilities by means of an object attached to the head.

Perceiving any environmental property requires spontaneously assembling a smart perceptual instrument-a task-specific measurement device assembled across potentially independent anatomical units. Previous research has shown that to a large degree, perception of a given environmental property is anatomically independent. We attempted to provide stronger evidence for this proposal by investigating perception by an organization of anatomical and inert components that likely requires the spontaneous assembly of a novel smart perceptual instrument-a rod attached to the head. Specifically, we compared cephalic and manual perception of whether an inclined surface affords standing on. In both conditions, perception reflected the action capabilities of the perceiver and not the appendage used to wield the rod. Such results provide stronger evidence for anatomical independence of perception within a given perceptual system and highlight that flexible task-specific detection units can be assembled across units that span the body and inert objects.

Pulling out all the stops to make the distance: Effects of effort and optical information in distance perception responses made by rope pulling.

Human observers perceive distance in remarkably stable and consistent manner across response methods and experimental paradigms. Most empirical work on the problem focused exclusively on geometrical variables, such as angle of declination below the horizon (Ooi, Wu, & He, 2001), with more recent considerations of nonvisual factors, such as effort (Proffitt, 2006). Hajnal, Bunch, and Kelty-Stephen (2014) showed that in addition to the object's physical angle of declination below the horizon, nonvisual variables related to effort were utilized when making distance estimates to objects placed on a sloped ramp. In that experiment, the horizontal ground surface was visible in the background when viewing objects placed on the sloped surface. To further investigate the joint utility of geometric and effort-based variables, we tested the effect of both classes of predictors on a natural hillside where a flat, horizontal surface was not visible in the background. This setup allowed us to evaluate whether observers rely on the same information to perceive distance on ramps versus real hills. The present research implicates the hypothesis that perceived effort and the geometry of space determine distance perception through interactions across multiple temporal scales of perceptual competence.

The Influence of Disclosure and Ethics Education on Perceptions of Financial Conflicts of Interest.

This study explored how disclosure of financial conflicts of interest (FCOI) influences naïve or "lay" individuals' perceptions of the ethicality of researcher conduct. On a between-subjects basis, participants read ten scenarios in which researchers disclosed or failed to disclose relevant financial conflicts of interest. Participants evaluated the extent to which each vignette represented a FCOI, its possible influence on researcher objectivity, and the ethics of the financial relationship. Participants were then asked if they had completed a college-level ethics course. Results indicated that FCOI disclosure significantly influenced participants' perceptions of the ethicality of the situation, but only marginally affected perceptions of researcher objectivity and had no significant influence on perceptions of the existence of FCOIs. Participants who had previously completed a college-level ethics course appeared more sensitive to the importance of FCOI disclosure than those who lacked such background. This result suggests that formal ethical training may help individuals become more critical consumers of scientific research.

Task specificity and anatomical independence in perception of properties by means of a wielded object.

Behavior is typically organized with respect to a goal to be achieved rather than the anatomical components used in doing so. Similarly, perception is typically organized with respect to a property to be perceived rather than the anatomical components used in doing so. Such task specificity and anatomical independence is manifest in perception of properties of a wielded object. In 6 experiments, we investigated whether these properties might also be manifest in perception of properties by means of a wielded object. In particular, we investigated perception of whether a surface could be stood on when the object used to explore that surface is wielded by the preferred and nonpreferred hands (Experiment 1), by 1 or both hands (Experiment 2), by different 2-handed grips (Experiment 3), and by entirely different limbs (i.e., the hand and the foot, Experiments 4-6). In general, the results show that perception reflected the action capabilities of the perceiver but was largely unaffected by the (configurations of) anatomical components used to wield the object. The results highlight the haptic system as a smart perceptual device and as a multifractal biotensegrity structure.

Getting off on the right (or left) foot: perceiving by means of a rod attached to the preferred or non-preferred foot.

Behavior is typically organized in terms of a goal one intends to achieve rather than in terms of the anatomical components used in doing so. Similarly, perceptual behavior is typically organized in terms of a property one intends to perceive rather than in terms of the anatomical components used in doing so. Such task-specificity and anatomical independence are manifest in perception of properties of wielded objects. We investigated whether these properties are also manifest in perception of properties by means of wielded objects. Blindfolded participants explored an inclined surface with a rod attached to their preferred or non-preferred foot and reported whether they would be able to stand on that surface. Perception reflected action capabilities, but was unaffected by foot used, highlighting the haptic system as a smart perceptual device.

Going for distance and going for speed: effort and optical variables shape information for distance perception from observation to response.

Visually guided distance perception reflects a relationship of geometrical optical variables with the effort required when traversing the distance. We probed how the representations encoding optical variables might define this relationship. Participants visually judged distances on sloped surfaces and reproduced these distances over flat terrain by walking while blindfolded. We examined the responses for the effects of optical variables (i.e., angular declinations from eye height) and tested whether four measures of trial-by-trial effort moderated the use of the represented optical variables. We predicted that observation time and response speed relative to the observed distance would accentuate the effects of encoded optical variables, and that response time and response speed relative to the traversed distance would reduce the effects of those variables. The results confirmed all of the effects except those of observation time. Given the benefits of longer study for strengthening a memory trace, the failure of observation time to predict the use of optical variables raises questions about the representational encoding of visual traces for distance perception. Relationships among optical variables and other effort measures implicate the interaction of processes across multiple time scales, as in cascade dynamics. Cascade dynamics may provide new directions for accounts of visually guided distance perception.

Location but not amount of stimulus occlusion influences the stability of visuomotor coordination.

The current study examined whether the amount and location of available movement information influenced the stability of visuomotor coordination. Participants coordinated a handheld pendulum with an oscillating visual stimulus in an inphase and antiphase manner. The effects of occluding different amounts of phase at different phase locations were examined. Occluding the 0°/180° phase locations (end-points) significantly increased the variability of the visuomotor coordination. The amount of occlusion had little or no affect on the stability of the coordination. We concluded that the end-points of a visual rhythm are privileged and provide access to movement information that ensures stable coordination. The results are discussed with respect to the proposal of Bingham (Ecol Psychol 16:45­43, 2004) and Wilson et al. (Exp Brain Res 165:351­361, 2005) that the relevant information for rhythmic visual coordination is relative direction information.

Transfer of calibration between hand and foot: functional equivalence and fractal fluctuations.

Transfer of competency in a perceptual task often depends on shared information between anatomically different perceptual subsystems. The problem of studying transfer involves isolating conditions of similarity and then trying to account for any resulting differences in transfer. To respect this twofold aspect, this article takes a two-pronged approach to transfer in dynamic touch. The present research first tests the hypothesis that functional equivalence supports the transfer of dynamic touch. Participants were trained to wield unseen objects with the hand or foot and were then tested on anatomically disparate limbs (i.e., the foot or hand, respectively). Next, we examined motion capture of these wielding behaviors for predictors of any asymmetry in transfer. Temporally fractal fluctuations of exploratory behavior can modulate information detection, and we tested whether the fractality of wielding might predict asymmetries in transfer across disparate limbs. Results suggest that transfer of training to anatomically disparate limbs respects functional conditions of similarity and also that the degree of temporally fractal fluctuations predicted limb differences in transfer.