Conflict in object affordance revealed by grip force

Viewing objects can result in automatic, partial activation of motor plans associated with them-"object affordance". Here, we recorded grip force simultaneously from both hands in an object affordance task to investigate the effects of conflict between coactivated responses. Participants classified pictures of objects by squeezing force transducers with their left or right hand. Responses were faster on trials where the object afforded an action with the same hand that was required to make the response (congruent trials) compared to the opposite hand (incongruent trials). In addition, conflict between coactivated responses was reduced if it was experienced on the preceding trial, just like Gratton adaptation effects reported in "conflict" tasks (e.g., Eriksen flanker). This finding suggests that object affordance demonstrates conflict effects similar to those shown in other stimulus-response mapping tasks and thus could be integrated into the wider conceptual framework on overlearnt stimulus-response associations. Corrected erroneous responses occurred more frequently when there was conflict between the afforded response and the response required by the task, providing direct evidence that viewing an object activates motor plans appropriate for interacting with that object. Recording continuous grip force, as here, provides a sensitive way to measure coactivated responses in affordance tasks.     

Separate Pathways for the Processing of Affordance of Neutral and Dangerous Object

Previous studies have shown that observation of object automatically elicits the activation of a reach-to-grasp response specifically directed to interact with the object, which is termed affordance. Recent findings provide evidences that even dangerous objects can evoke aversive affordances. However, these studies only focused on avoidance effect emerged with dangerous objects. It remains unclear whether the neutral object and dangerous object share a common mechanism for the processing of affordance information. The affordance effect is considered to be a type of conflict between the afforded response and the response required by the task. In a symbol judgment task, we simultaneously presented the neutral object and dangerous object to investigate whether the congruency sequence effects (congruency effects following incongruent trials are smaller than those following congruent trials) occurred across the two types of affordance conflict, which is typically assumed that such flexible adjustments can only be observed between the same conflict types. It was found that congruency sequence effects were only generated between the same types of affordance conflict (e.g., neutral object or dangerous object), but not between two different affordance conflict types (e.g., neutral object and dangerous object). These results indicate there may be two different pathways for the processing of affordance of the neutral and dangerous object.     

Modulation of the affordance effect through transfer of learning

Consistent evidence shows that practising with spatially incompatible stimulus–response trials modulates performance on following tasks requiring the solution of cognitive conflict such as the Simon and Stroop tasks. In the present study we assessed whether a spatially incompatible practice can modulate another effect that is thought to be due to a conflict between two response alternatives, the affordance effect. To this end, we requested participants to categorize pictures of common objects on the basis of their upright or inverted orientation. A group of participants performed the categorization task alone, while the other two groups performed the categorization task after practising with a spatial compatibility task with either a compatible or an incompatible mapping. Results showed that the spatially incompatible practice eliminated the affordance effect. These results indicate that the conflict at the basis of the affordance effect is not unavoidable but it rather permeable to modulations affecting the response selection stage. Indeed the “emit the alternative spatial response” rule acquired during the spatially incompatible task can transfer to and modulate how the subsequent affordance task is performed.     

Viewing objects and planning actions: on the potentiation of grasping behaviours by visual objects

How do humans interact with tools? Gibson (1979) suggested that humans perceive directly what tools afford in terms of meaningful actions. This “affordances” hypothesis implies that visual objects can potentiate motor responses even in the absence of an intention to act. Here we explore the temporal evolution of motor plans afforded by common objects. We presented objects that have a strong significance for action (pinching and grasping) and objects with no such significance. Two experimental tasks involved participants viewing objects presented on a computer screen. For the first task, they were instructed to respond rapidly to changes in background colour by using an apparatus mimicking precision and power grip responses. For the second task, they received stimulation of their primary motor cortex using transcranial magnetic stimulation (TMS) while passively viewing the objects. Muscular responses (motor evoked potentials: MEPs) were recorded from two intrinsic hand muscles (associated with either a precision or power grip). The data showed an interaction between type of response (or muscle) and type of object, with both reaction time and MEP measures implying the generation of a congruent motor plan in the period immediately after object presentation. The results provide further support for the notion that the physical properties of objects automatically activate specific motor codes, but also demonstrate that this influence is rapid and relatively short lived.     

Electromyographic evidence for response conflict in the exclude recognition task

How do memory retrieval processes lead to overt responses in strategic recognition tasks (responding “old” to one class of familiar stimulus and “new” to another)? Many current theories of memory retrieval ignore the response requirements in such memory tasks, instead modeling them using memory processes (e.g., familiarity and recollection) alone (see Yonelinas, 2002). We argue that strategic recognition involves conflict in response processing similar to canonical conflict tasks (e.g., the Stroop task). The parallel task set (PTS) model (Seymour, 2001) accounts for performance in strategic recognition tasks (e.g., the exclude recognition task) by suggesting that motor response conflict occurs when one responds “new” to familiar stimuli. We tested this prediction using surface electromyography, a measure incontrovertibly related to motor execution. Overall, results are consistent with the PTS model’s assumption that recognition, motor, and control processes interact in strategic retrieval tasks. The implications of these data for models of memory retrieval and response conflict are discussed.     

Grasping the pain: Motor resonance with dangerous affordances

Two experiments, one on school-aged children and one on adults, explored the mechanisms underlying responses to an image prime (hand vs. control object) followed by graspable objects that were, in certain cases, dangerous. Participants were presented with different primes (a male, a female and a robotic grasping-hand; a male and a female static-hand; a control stimulus) and objects representing two risk levels (neutral and dangerous). The task required that a natural/artifact categorization task be performed by pressing different keys. In both adults and children graspable objects activated a facilitating motor response, while dangerous objects evoked aversive affordances, generating an interference-effect. Both children and adults were sensitive to the distinction between biological and non-biological hands, however detailed resonant mechanisms related to the hand-prime gender emerged only in adults. Implications for how the concept of “dangerous object” develops and the relationship between resonant mechanisms and perception of danger are discussed.     

Binocular vision enhances a rapidly evolving affordance priming effect: Behavioural and TMS evidence

Extensive research has suggested that simply viewing an object can automatically prime compatible actions for object manipulation, known as affordances. Here we explored the generation of covert motor plans afforded by real objects with precision (‘pinchable’) or whole-hand/power (‘graspable’) grip significance under different types of vision. In Experiment 1, participants viewed real object primes either monocularly or binocularly and responded to orthogonal auditory stimuli by making precision or power grips. Pinchable primes facilitated congruent precision grip responses relative to incongruent power grips, and vice versa for graspable primes, but only in the binocular vision condition. To examine the temporal evolution of the binocular affordance effect, participants in Experiment 2 always viewed the objects binocularly but made no responses, instead receiving a transcranial magnetic stimulation pulse over their primary motor cortex at three different times (150, 300, 450 ms) after prime onset. Motor evoked potentials (MEPs) recorded from a pinching muscle were selectively increased when subjects were primed with a pinchable object, whereas MEPs from a muscle associated with power grips were increased when viewing graspable stimuli. This interaction was obtained both 300 and 450 ms (but not 150 ms) after the visual onset of the prime, characterising for the first time the rapid development of binocular grip-specific affordances predicted by functional accounts of the affordance effect.     

Binocular vision enhances a rapidly evolving affordance priming effect: Behavioural and TMS evidence

Extensive research has suggested that simply viewing an object can automatically prime compatible actions for object manipulation, known as affordances. Here we explored the generation of covert motor plans afforded by real objects with precision (‘pinchable’) or whole-hand/power (‘graspable’) grip significance under different types of vision. In Experiment 1, participants viewed real object primes either monocularly or binocularly and responded to orthogonal auditory stimuli by making precision or power grips. Pinchable primes facilitated congruent precision grip responses relative to incongruent power grips, and vice versa for graspable primes, but only in the binocular vision condition. To examine the temporal evolution of the binocular affordance effect, participants in Experiment 2 always viewed the objects binocularly but made no responses, instead receiving a transcranial magnetic stimulation pulse over their primary motor cortex at three different times (150, 300, 450 ms) after prime onset. Motor evoked potentials (MEPs) recorded from a pinching muscle were selectively increased when subjects were primed with a pinchable object, whereas MEPs from a muscle associated with power grips were increased when viewing graspable stimuli. This interaction was obtained both 300 and 450 ms (but not 150 ms) after the visual onset of the prime, characterising for the first time the rapid development of binocular grip-specific affordances predicted by functional accounts of the affordance effect.     

Motor inhibition associated with the affordance of briefly displayed objects

Research has demonstrated that left- and right-hand responses are facilitated when they are performed with the hand compatible with the orientation of a viewed object. This suggests that graspable objects automatically activate the motor representations that correspond to their orientation. It has recently been proposed that similar positive stimulus–response compatibility effects (PCE) may turn into negative compatibility effects (NCE) when a prime object is displayed very briefly. These NCEs are suggested to reflect motor inhibition mechanisms—motor activation triggered by briefly viewed objects may be treated by the motor system as unwanted, and thus it is rapidly inhibited. We examined whether the motor activation triggered by the orientation of a task-irrelevant object is similarly inhibited when the object is displayed briefly. In Experiment 1, a NCE was observed between the orientation of an object and the responding hand when the object was displayed for 30 or 70 ms. The effect turned into a PCE when the object was displayed for 370 ms. Experiment 2 confirmed that this motor inhibition effect was produced by the handle affordance of the object rather than some abstract visual properties of the object.     

Word‐to‐picture recognition is a function of motor components mappings at the stage of retrieval

Embodied approaches of cognition argue that retrieval involves the re‐enactment of both sensory and motor components of the desired remembering. In this study, we investigated the effect of motor action performed to produce the response in a recognition task when this action is compatible with the affordance of the objects that have to be recognised. In our experiment, participants were first asked to learn a list of words referring to graspable objects, and then told to make recognition judgements on pictures. The pictures represented objects where the graspable part was either pointing to the same or to the opposite side of the “Yes” response key. Results show a robust effect of compatibility between objects affordance and response hand. Moreover, this compatibility improves participants' ability of discrimination, suggesting that motor components are relevant cue for memory judgement at the stage of retrieval in a recognition task. More broadly, our data highlight that memory judgements are a function of motor components mappings at the stage of retrieval.     

The predictive mirror: interactions of mirror and affordance processes during action observation

An important question for the study of social interactions is how the motor actions of others are represented. Research has demonstrated that simply watching someone perform an action activates a similar motor representation in oneself. Key issues include (1) the automaticity of such processes, and (2) the role object affordances play in establishing motor representations of others' actions. Participants were asked to move a lever to the left or right to respond to the grip width of a hand moving across a workspace. Stimulus-response compatibility effects were modulated by two task-irrelevant aspects of the visual stimulus: the observed reach direction and the match between hand-grasp and the affordance evoked by an incidentally presented visual object. These findings demonstrate that the observation of another person's actions automatically evokes sophisticated motor representations that reflect the relationship between actions and objects even when an action is not directed towards an object.     

Action priming by briefly presented objects

Three experiments investigated how visual objects prime the actions they afford. The principal concern was whether such visuomotor priming depends upon a concurrent visual input--as would be expected if it is mediated by on-line dorsal system processes. Experiment 1 showed there to be essentially identical advantages for making afforded over non-afforded responses when these were made to objects still in view and following brief (30 or 50 ms) object exposures that were backward masked. Experiment 2 showed that affordance effects were also unaffected by stimulus degradation. Finally, Experiment 3 showed there to be statistically equal effects from images of objects and their names. The results suggest that an active object representation is sufficient to generate affordance compatibility effects based on associated actions, whether or not the object is concurrently visible.     

Motor learning of cue-dependent pull-force changes during an isometric precision grip task

The “raspberry task” represents a precision grip task that requires continuous adjustment of grip and pull forces. During this task subjects grip a specialized grip rod and have to increase the pull force linearly while the rod is locked. The aim of this study was to determine whether an associated, initially neutral cue is able to evoke pull-force changes in the raspberry task. A standard delay paradigm was used to study cued pull-force changes during an ongoing movement resulting in unloading. Pull force and EMG activity of hand and arm muscles were recorded from 13 healthy, young subjects. The cue was associated with a complex change in motor behavior.In this task, cued force changes take place more rapidly than in protective reflex systems (in median after the second presentation of the cueing stimulus). A cued force change was detectable in two-thirds of paired trials. Although the force change is produced by a decrease of the EMG activity in several grip- and pull-force-producing muscles, the most significant effect in the majority of the subjects was an increase of the activity of the flexor carpi ulnaris muscle which antagonises corresponding pull-force-producing muscles. Cued force changes require adequately and precisely controlled activation of the muscle groups involved in the movement.     

S-R correspondence effects of irrelevant visual affordance: Time course and specificity of response activation

It has been suggested that representations for action, elicited by an object's visual affordance, serve to potentiate motor components (such as a specific hand) to respond to the most afforded action. In three experiments, participants performed speeded left-right button press responses to an imperative target superimposed onto a prime image of an object suggesting a visual affordance oriented to left or right visual space. The time course of response activation was measured by varying the onset time between the prime and target. Long-lasting and gradually developing correspondence effects were found between the suggested affordance of the prime and the side of response, with little effect of response modality (hands uncrossed, hands crossed, or foot response). We conclude that visual affordances can evoke an abstract spatial response code, potentiating a wide variety of lateralized responses corresponding with the affordance.     

行动语义、客体背景和判断任务对客体动作承载性的影响

客体动作承载性指人们知觉客体时同时激活的针对客体的行动。当Gibson最初提出动作承载性概念时, 他认为客体的这种属性是可以自动激活的。然而近年来越来越多的证据显示, 在知觉和行动的关系中, 行动语义知识和客体所处背景对客体动作承载性具有调节作用, 表现在人们可以根据这些自上而下的信息选择针对客体的适当的行动。此外, 不同的判断任务在引发客体动作承载性效应上具有特异性, 表现在若判断任务仅需知觉客体表层属性时, 不能激活对客体的动作, 进而不能产生客体动作承载性; 若判断任务需要对客体进行深层加工时, 才会激活对客体的动作。未来研究还需要进一步探究行动语义知识和客体所处背景影响客体动作承载性发生的原因和机制, 以及不同判断任务中出现结果特异性的原因。     

Response interference between functional and structural actions linked to the same familiar object

Viewing objects with the intention to act upon them may activate task-irrelevant motor responses. Many manufactured objects are associated with two action classes: grasping in accordance with object structure and skillful use consistent with object function. We studied the potential for within-object competition during action selection by comparing initiation latencies for “conflict” objects (with competing structure and function responses) to “non-conflict” objects (with a single response). We demonstrated a novel pattern of within-object interference wherein actions involving conflict objects were slowed when participants skillfully used those objects (grasp-on-use interference) as well as a second pattern of interference when conflict objects were grasped after skillfully using the same objects in previous blocks (long-term use-on-grasp interference). These data suggest that actions to common objects are influenced by competition between rapid but briefly maintained grasp responses and slower but longer-lasting use responses, and advance our understanding of the process and neural substrates of selection for action.     

Electrophysiological examination of embodiment in vision and action

A wealth of behavioral data has shown that the visual properties of objects automatically potentiate motor actions linked with them, but how deeply are these affordances embedded in visual processing? In the study reported here, we used electrophysiological measures to examine the time course of affordance resulting from the leftward or rightward orientation of the handles of common objects. Participants were asked to categorize those objects using a left- or right-handed motor response. Lateralized readiness potentials showed rapid motor preparation in the hand congruent with the affordance provided by the object only 100 to 200 ms after stimulus presentation and up to 400 ms before the actual response. Examination of event-related potentials also revealed an effect of handle orientation and response-hand congruency on the visual P1 and N1 components. Both of these results suggest that activity in the early sensory pathways is modulated by the action associations of objects and the intentions of the viewer.     

Bimanual Lifting: Do Fingertip Forces Work Independently or Interactively?

Bimanual coordination is a commonplace activity, but the consequences of using both hands simultaneously are not well understood. The authors examined fingertip forces across 4 experiments in which participants undertook a range of bimanual tasks. They first measured fingertip forces during simultaneous lifts of 2 identical objects, noting that individuals held the objects with more force bimanually than unimanually. They then varied the mass of the objects held by each hand, noting that when both hands lifted together performance was equivalent to unimanual lifts. The authors next measured one hand's static grip force while the other hand lifted an object. They found a gradual reduction of grip force throughout the trial, but once again no evidence of one hand influencing the other. In the final experiment the authors tested whether tapping with one hand could influence the static grip force of its counterpart. Although the authors found no changes in static grip force as a direct consequence of the other hand's actions, they found clear differences from one task to the other, suggesting an effect of task instruction. Overall, these results suggest that fingertip forces are largely independent between hands in a bimanual lifting context, but are sensitive to different task requirements.     

Sensorimotor fluency influences affect: Evidence from electromyography

Fluency of visual processing induces affective responses, with easier-to-process stimuli being preferred (Winkielman & Cacioppo, 2001). The present study extends this research to the motor domain by investigating the effect of sensorimotor fluency on affective reactions to objects in a categorisation task. In fluent stimulus–response (s–r) trials, grasp-compatible objects were presented on the same side of the screen as the response hand; in non-fluent trials, grasp incompatible objects were presented on the opposite side of the screen to the response hand. Affective responses were measured implicitly using face muscle activity (electromyography). As predicted, participants exhibited greater cheek muscle activity (associated with smiling) in trials with s–r compatible responses compared with incompatible responses. These findings support hedonic models of fluency in which fluent processing elicits direct emotional experience, and suggest that models of hedonic fluency should take into account the integration of the motor system in visual processing.     

Action representations activated by task‐irrelevant information: Is it really irrelevant?

Accessing action knowledge is believed to rely on the activation of action representations through the retrieval of functional, manipulative, and spatial information associated with objects. However, it remains unclear whether action representations can be activated in this way when the object information is irrelevant to the current judgment. The present study investigated this question by independently manipulating the correctness of three types of action‐related information: the functional relation between the two objects, the grip applied to the objects, and the orientation of the objects. In each of three tasks in Experiment 1, participants evaluated the correctness of only one of the three information types (function, grip or orientation). Similar results were achieved with all three tasks: “correct” judgments were facilitated when the other dimensions were correct; however, “incorrect” judgments were facilitated when the other two dimensions were both correct and also when they were both incorrect. In Experiment 2, when participants attended to an action‐irrelevant feature (object color), there was no interaction between function, grip, and orientation. These results clearly indicate that action representations can be activated by retrieval of functional, manipulative, and spatial knowledge about objects, even though this is task‐irrelevant information.