Edited by: Diana M. E. Torta, University of Turin, Italy
Reviewed by: Michael Schaefer, University Magdeburg, Germany; Susanne Becker, Central Institute of Mental Health, Germany
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Behavioral and neuroscience studies have shown that objects observation evokes specific affordances (i.e., action possibilities) and motor responses. Recent findings provide evidence that even dangerous objects can modulate the motor system evoking aversive affordances. This sounds intriguing since so far the majority of behavioral, brain imaging, and transcranial magnetic stimulation studies with painful and dangerous stimuli strictly concerned the domain of pain, with the exception of evidence suggesting sensitivity to objects’ affordances when neutral objects are located in participants’ peripersonal space. This study investigates whether the observation of a neutral or dangerous object in a static or dynamic situation differently influences motor responses, and the time-course of the dangerous objects’ processing. In three experiments we manipulated: object dangerousness (neutral vs. dangerous); object category (artifact vs. natural); manual response typology (press vs. release a key); object presentation (Experiment 1: dynamic, Experiments 2 and 3: static); object movement direction (Experiment 1: away vs. toward the participant) or size (Experiments 2 and 3: big vs. normal vs. small). The task required participants to decide whether the object was an artifact or a natural object, by pressing or releasing one key. Results showed a facilitation for neutral over dangerous objects in the static situation, probably due to an affordance effect. Instead, in the dynamic condition responses were modulated by the object movement direction, with a dynamic affordance effect elicited by neutral objects and an escape-avoidance effect provoked by dangerous objects (neutral objects were processed faster when they moved toward-approached the participant, whereas dangerous objects were processed faster when they moved away from the participant). Moreover, static stimuli influenced the manual response typology. These data indicate the emergence of dynamic affordance and escaping-avoidance effects.
In our lives we constantly interact with different kinds of objects, characterized by different features, and we need to learn their properties. For example, so far literature investigated the importance of size (e.g., Tucker and Ellis,
Since Gibson (
As for humans, similar results have been obtained with brain activation studies (for a review, see Martin,
In addition to these findings, several cognitive behavioral studies have demonstrated that overt reaching and grasping movements can be activated during objects observation (for reviews, see Borghi and Cimatti,
One line of research particularly relevant to the issue addressed in our study concerns the relation between affordances and space. In a series of studies, Costantini and colleagues tried to clarify whether affordances differently emerged when objects, as for example bottles, were located within or outside the perceiver’s peripersonal space, namely in the space that encompassed the objects within reach (Rizzolatti et al.,
Another line of research deserves to be introduced, namely studies aimed at investigating responses induced by the observation of others’ pain. In a seminal study, Singer et al. (
In addition, in a series of TMS studies Avenanti et al. (
Not only neural, but also behavioral evidence demonstrated a specific influence of pain observation on overt motor responses. A study of Morrison et al. (
On the whole, these findings reveal the emergence of resonance mechanisms when pain was passively induced by an object and participants could observe the direct interaction between a hand and a needle (see Haggard et al.,
Thus, so far several works demonstrated that participants tend to respond to objects’ affordances, and a variety of behavioral, brain imaging, and TMS studies with painful and dangerous stimuli were carried out in the domain of pain investigation. These two lines of research were merged in some recent behavioral studies on affordances and dangerous objects. Interestingly, recent evidence revealed that not only pleasant and neutral objects but also dangerous objects activate motor information during our interaction with them. In previous investigations (Anelli et al.,
Along this line of research, in a subsequent study (Anelli et al.,
To sum up, recent evidence suggests that even dangerous objects can modulate the motor system evoking aversive affordances, i.e., inducing the tendency to avoid dangerous objects. The research area about aversive affordances represents a new and intriguing research field, since so far the majority of studies with painful and dangerous stimuli strictly concerned the domain of pain investigation.
In the present work we focus on some unanswered questions on aversive affordances, by investigating object dangerousness without considering motor resonance mechanisms, and by exploring whether and how the observation of a neutral or dangerous object, in a static or dynamic situation, can differently modulate our motor responses.
First of all, previous studies investigated how motor responses were influenced by object dangerousness, but limited their focus to situations in which objects were preceded by hands in potential interaction with them, thus generating a motor resonance effect (e.g., Anelli et al.,
Second, in the literature static images are usually presented. Since objects/entities are typically threatening when they approach us, we chose to employ a more dynamic and ecologically rich experimental setting, by showing stimuli in dynamic scenes. This more natural embedding allows us to take into account the spatial relationship between stimuli and subject, and thus to consider dangerousness no longer as an objective property, but as a relational one.
Third, so far some aforementioned studies (e.g., Costantini et al.,
Fourth, it can be posited that different response modalities subtend different motor actions, and specifically key-releases can underlie withdrawal movements and key-presses can underlie approach movements. So far Morrison et al. (
Finally, even if a couple of studies (Lloyd et al.,
To explore these issues, we conducted three experiments requiring participants to perform a simple categorization task, i.e. to decide whether the stimulus shown was an artifact or a natural object. To respond they were required to either press or release one of two designed keys, observing objects in dynamic (Experiment 1) or static (Experiments 2 and 3) conditions. As in our previous works, we focused on how dangerous and neutral objects are perceived and processed at a motor level. We were not interested in the distinction between risk for pain and threat, but in the motor responses evoked by the observation of objects or entities that can potentially provoke pain, independently of their being active or passive.
The aims of the study and our predictions are the following. First, we aim to investigate the sensitivity to objects dangerousness and the emergence of related affordances without showing somebody in
Second, we focus on the impact of neutral and dangerous objects when they come toward us (dynamic presentation) or when they are close to us (static presentation) with respect to when they go away from us (dynamic presentation) or when they are distant from us (static presentation).
Third, and related to previous point, we intend to clarify how static and dynamic objects’ presentations influence the response to neutral vs. dangerous objects, and whether there is a modulation due to the response modality (key press vs. release). We hypothesize that motor responses would be facilitated, and thus response times would be faster, with dynamic than with static presentations with dangerous objects and release response, due to the fact that humans might tend to escape from dangerous objects and entities as soon as possible, particularly when they have an aggressive behavior.
Fourth, we investigate the time-course of the process, and thus whether the processing of dangerous objects allows immediate responses or whether it requires to prepare responses, also considering the object’s distance. Indeed, notice that distance and time are related: when we can see dangerous entities from far away, we have time to prepare our responses; this is not the case when these entities are very close to us. We do not advance a precise prediction on this point, but our aim is to examine the time-course of dangerous objects processing.
Finally, in light of our previous studies (Anelli et al.,
The aim of the first experiment was to investigate whether participants were sensitive to differences in the direction of object movement. In particular, we intended to verify if observing a dangerous or a neutral object in a dynamic situation (i.e., a video of an object moving away or near to the participant) can differently influence the motor responses. In addition, we considered how motor responses can be modulated by the considered variables at different ages, by testing both children and adults.
To these aims, we ran an experiment in which participants were required to distinguish between an artifact and a natural object, so that the object dangerousness and movement direction were not relevant to the task.
Fourteen undergraduate students from the University of Bologna (six males and eight females, mean age: 20.7 years, range: 19–27) and 14 children (seven males and seven females; mean age: 11.2 years, range: 10–12), took part in the experiment. All participants were right-handed and had normal or corrected-to-normal vision. All were naive as to the purpose of the experiment and they or their parents, as for children, gave informed consent. The present and the following experiments were approved by the Psychology Department’s ethical committee of the University of Bologna.
Participants sat in front of a 17″ color monitor (the eye-to-screen distance was approximately 50 cm). E-Prime 2.0 software was used for presenting stimuli and collecting responses.
The experimental stimuli consisted of 16 color pictures of common graspable objects (see Table
Neutral objects | Dangerous objects | |
---|---|---|
Natural objects | Cat | Porcupine |
Chick | Scorpio | |
Plant | Cactus | |
Tomato | Husk | |
Artifact objects | Bulb | Broken bulb |
Glass | Broken glass | |
Lighted out match | Lighted match | |
Spoon | Knife |
Participants were required to decide whether the stimulus was an artifact or a natural object, so that the
The experiment consisted of one practice block of 16 trials and one experimental block of 128 trials. Each trial began with a fixation point (+) displayed for 500 ms in the center of the screen. Then, the video of a moving object was shown for 1000 ms and followed by a static picture of the object (of the same size of the last video frame) containing the go-signal (a green circle) that remained on the center of the screen until a response had been made or 2000 ms had elapsed. Participants received feedback on reaction time (RT) after pressing the right or the wrong key (the RT value or “Error,” respectively). The next trial began after the feedback disappeared.
Each object was presented eight times: during half of the presentation the object moved away from the participant, with a progressive zoom out of the object, while in the other half the object moved toward the participant, with a progressive zoom of the object.
Overall the experiment consisted of 144 trials and lasted about 20 min.
Reaction times for incorrect responses and RTs more than two standard deviations from each participant’s overall mean were excluded from the analysis.
The correct RTs were entered into a repeated-measures ANOVA with
The interaction between
Furthermore, the interaction between
There were no other significant main effects or interactions (
Results showed that, in a dynamic condition, responses were specifically influenced by the object movement direction in a twofold way. First, the movement direction affected the processing of objects belonging to different typologies, since neutral objects were processed faster when moving toward-approaching the participant. This effect can be considered as a dynamic affordance effect. In contrast, we found that dangerous objects were processed faster when moving away from the participant. The longer RTs with dangerous objects when they approached participants are probably due to a blocking effect. We will discuss this issue more thoroughly in the Section “
Second, the object movement direction also modulated the processing of object category, since responses to artifact objects were faster when moving toward-approaching the participant. This finding adds to previous one as a further demonstration of a dynamic affordance effect, which emerges with a specific category, that of artifact objects. As shown in previous studies, this is likely due to artifact objects activation both of the tendency to manipulate them and to use them, differently from natural objects that convey only information related to manipulation (e.g., Borghi et al.,
To note, in this experiment we did not register any influence of manual response typology on motor responses. This could either indicate that the employed types of manual response are not effective or that the absence of effects can be rather attributed to the modality of stimuli presentation. We favored the latter interpretation that would imply that, in a dynamic condition, the movement direction of objects became more important than the different motor responses (i.e., press vs. release) at the disposal of participant. The next experiments will allow us to verify these two alternative hypotheses, since we presented objects in a static condition. If, in line with our second explanation, in Experiments 2 and/or 3 the effect of manual response typology will be present, this would mean that it effectively has a different role depending on the modality of objects presentation.
A final point deserved our consideration: the lack of influence of different age classes we considered, namely children and adults. These data allowed us to speculate that object dangerousness represents a salient object’s property, probably because it is adaptive to learn to quickly distinguish between neutral and dangerous objects early on during development. This explanation fits well also with previous evidence on school-age children showing their early sensitivity to object dangerousness and the emergence later in life of more subtle differences, such as those related to object category (Anelli et al.,
Experiment 2 was aimed at understanding what happened when participants observed dangerous or neutral objects in a static situation, rather than in a dynamic one. The task was the same of the previous experiment, i.e. participants were required to distinguish between an artifact and a natural object. To note, in order to explore the time-course of dangerousness processing, participants had time to process objects and to prepare their motor responses: we presented a static picture of an object for 1 s before the appearance of another static picture of the same object containing the go-signal to respond. As explained above, here and in the next experiment we collected only data on adults.
Sixteen undergraduate students from the University of Bologna (3 males and 13 females, mean age: 19.8 years, range: 19–25) took part in Experiment 2 for course credits. All participants were right-handed and had normal or corrected-to-normal vision. All were naive as to the purpose of the experiment and gave informed consent.
The stimuli and the task were the same of previous experiment. However, in the present experiment, participants observed the objects in a static situation, whereas during Experiment 1 the objects were presented in a dynamic situation.
The experiment consisted of one practice block of 12 trials and one experimental block of 192 trials. Each trial began with a fixation point (+) displayed for 500 ms in the center of the screen. Then, the static picture of an object was shown for 1000 ms and followed by another static picture of the same object containing the go-signal (a green circle) that remained on the center of the screen until a response had been made or 2000 ms had elapsed. Participants received feedback on RT after pressing the right or the wrong key (the RT value or “Error,” respectively). The next trial began after the feedback disappeared.
Each object was presented 12 times: in one-third of the trials the object with the go-signal was larger than the first static picture (big size condition), in one-third it remained of the same size of the first static picture (normal size condition), and in the other-third it was smaller than the first static picture (small size condition). In the big size and in the small size conditions, the object with the go-signal had the same size of the last frame of the video clip shown in Experiment 1 (toward and away conditions, respectively).
Overall the experiment consisted of 204 trials and lasted about 25 min.
The data were treated according to the same criteria used for Experiment 1. RTs for incorrect responses and RTs more than two standard deviations from each participant’s overall mean were excluded from the analysis.
The correct RTs were entered into a repeated-measures ANOVA with
The main effects of
Results revealed that participants were sensitive to the objects’ dangerousness, as response times were faster with neutral than with dangerous objects. In line with our hypothesis, this evidence pointed out the influence of a fine object property such as object dangerousness on motor responses. In line with our previous data (Anelli et al.,
In addition, we registered an effect of the objects’ size, as response times were faster with big than with normal and small objects. Two explanations were possible. The first referred simply to a perceptual effect, so that larger objects were processed faster than smaller ones. The second, and more interesting to us, explained this effect not only as visual but as motor as well. In this latter case, objects would evoke faster motor responses since grasping larger objects is less complex than grasping smaller ones (e.g., Bazzarin et al.,
One final aspect is worth noticing: we did not find any effect of the object category, in contrast with previous experiment and with the majority of the studies on this issue. Even if we cannot say much about a null result, we can speculate that this was due to the fact that the distinction between dangerous and neutral objects was much more salient, and washes out the distinction between an artifact and a natural object.
Experiment 3 was a control experiment. The only difference from Experiment 2 was that participants were required to discriminate between an artifact and a natural object as soon as the object appeared on the screen, so that an immediate coding of the stimulus was required. Along with previous data, this manipulation allowed us to verify the time-course of sensitivity both to objects dangerousness and objects size, and to clarify the motor vs. perceptual features of the effect size emerged in previous experiment.
Sixteen undergraduate students from the University of Bologna (5 males and 11 females, mean age: 20.3 years, range: 19–26) took part in Experiment 3 for course credits. As in previous experiments, all subjects were right-handed and had normal or corrected-to-normal vision. All were naive as to the purpose of the experiment and gave informed consent.
The apparatus and stimuli were the same used in Experiment 2. The only difference was that participants were instructed to respond as soon as the object appeared.
Each trial began with a fixation point (+) displayed for 500 ms in the center of the screen. Soon after, the static picture of an object containing the go-signal (a green circle) was shown until a response had been made or 2000 ms had elapsed. Participants received feedback on RT after pressing the right or the wrong key (the RT value or “Error,” respectively). The next trial began after the feedback disappeared.
Each object was presented 12 times: in one-third of the trials the object with the go-signal was large (big size condition), in one-third it had a normal size (normal size condition), and in the other-third it was small (small size condition). In the big size and in the small conditions, the object with the go-signal had the same size of the last frame of the video clip showed in Experiment 1 (near and away conditions, respectively) and of the second object showed in Experiment 2.
Overall the experiment consisted of 204 trials and lasted about 25 min.
The data were treated according to the same criteria used for previous experiments. RTs for incorrect responses and RTs more than two standard deviations from each participant’s overall mean were excluded from the analysis.
The correct RTs were entered into a repeated-measures ANOVA with
The main effect of
The interaction between
In keeping with what found in Experiment 2, participants responded faster to neutral objects than to dangerous ones.
Interestingly, participants were not sensitive to the objects’ size, in contrast to what happened in Experiment 2. Most crucial for us was the significant interaction between
In addition, this interaction helped to interpret the results of the previous experiment clarifying that the size effect was not simply a perceptual one, but was motor as well. Indeed, it seemed to imply the tendency to grasp neutral objects and to escape from dangerous objects.
Further, the difference between Experiments 2 and 3 allowed us to speculate that the size effect can be influenced by the time that participants had at their disposal to respond. In fact, when they had a brief delay (1 s) before responding, as in Experiment 2, and thus they can prepare a motor response, it is possible that they process information related to dangerousness and size in a separate fashion. On the contrary, when an immediate response was required, and thus participants cannot prepare a motor response, as in Experiment 3, they could process information on dangerousness in strict relation to information on size. This indicated that participants were able to integrate different kinds of information rather quickly when rapid responses were required.
In the present study we investigate whether motor responses are influenced by the observation of object dangerousness in dynamic and static situations, without showing a direct or potential interaction between an object and an effector. In three experiments we focused on the conceptual distinction between neutral and dangerous objects, by asking participants to perform a simple categorization task (i.e., to decide whether the stimulus shown was an artifact or a natural object), by pressing or releasing one of two designed keys. The object size was manipulated in order to provide a cue indicating distance, namely smaller objects indicated objects more distant from the participant’s body, whereas larger objects indicated objects closer to the participant. The object presentation could be dynamic (Experiment 1) or static (Experiments 2 and 3), as objects moved toward or away from participants (dynamic presentation) or objects were close or distant from participants (static presentation). Moreover, time-course has been considered, by investigating whether the processing of dangerousness differed depending on whether time to prepare motor responses was given (Experiments 1 and 2) or whether an immediate motor response was required (Experiment 3).
In Experiment 1 both children and adults were tested, while in Experiment 2 and 3 the sample was composed only by adults. Despite the complexity of our experimental design, our results are quite consistent across experiments. We will discuss them below.
First of all, results of all three experiments showed that participants were sensitive to the difference between dangerous and neutral objects, in line with our previous data (Anelli et al.,
The present work allowed us to advance some speculations about the possible neural mechanisms involved in the processing of neutral and dangerous objects. To note, differently from previous behavioral and TMS studies (e.g., Avenanti et al.,
The second interesting result of our study concerns the influence of the spatial relationship between stimuli and subject on the objects’ processing. Our data revealed that participants’ responses were influenced by the kind of object movement direction in a dynamic condition (Experiment 1). In particular, neutral objects were processed faster when they moved toward-approached the participant than when they moved away from her. This result seemed to be in keeping with data showing the emergence of affordances only when objects were located within the perceiver’s or observer’s peripersonal space (Costantini et al.,
On the whole, these findings demonstrated the emergence of selective motor effects related to different objects typologies, modulated by the object movement direction in the space and not by actions performed by an observed agent. It is worth noting that in this way dangerousness was considered as a relational property of objects, namely as a property which is neither of the object/environment nor of the acting organism, in keeping with the definition of affordances as intrinsically relational properties.
These results can be of particular interest since so far, to our knowledge, even if a number of studies investigated the relationship between object affordances and space (e.g., Costantini et al.,
A third result concerned the influence of manual response typology. When the object presentation was dynamic (Experiment 1) motor responses were not influenced at all by manual response typology, raising the possibility that the manipulation employed was not effective. Instead, data of Experiment 3, when the objects presentation was static, demonstrated that this was not the case, since two different effects have been registered. On one hand, a facilitation effect emerged when key press responses concerned neutral objects, probably linked to an affordance effect evoked by this kind of objects with a response modality associated to approach movements. On the other hand, key release responses led to a higher interference effect with large dangerous objects, probably due to a tendency to escape evoked by this kind of objects with a response modality associated to withdrawal movements. This finding was in line with the results of Morrison et al. (
On the whole, findings on manual response typology point out the influence of the modality of objects presentation on the emergence of facilitation and interference effects. In fact, in the dynamic condition the movement direction of objects becomes more salient for the participants than their own actions. Conversely, in the static condition the manual response typology becomes relevant, as participants perceived the importance of their own specific actions in order to interact with objects or to avoid them.
As final point, the investigation of the time-course revealed that the processing of dangerousness was influenced by the amount of time that participants had at their disposal to respond. In this respect, the interaction between the three main factors found in Experiment 3, in which no time for action preparation was given, was particularly informative. Indeed, this interaction showed that, while with key press responses small dangerous objects were the slowest items to be processed, with key release responses the slowest items were large dangerous objects. This qualified the interference effect found in previous studies (Anelli et al.,
The situation was quite different when there was time for response preparation (1 s delay). Indeed, in Experiment 2, while the advantage of neutral over dangerous objects was present, there was no interaction and overall large objects were processed faster than small ones. One possibility was that the effect was due mostly to neutral objects; a qualitative analysis suggested this was the case, but the result was far from significance.
The results of Experiment 1 can help us to better comprehend the data. In fact, the advantage of the toward condition (in which the last video frame depicted large objects) was confined to neutral objects, probably due to an affordance effect, i.e. the tendency to grasp neutral objects, that was stronger when objects were approaching. Instead, the advantage of the away condition (in which the last video frame depicted small objects) concerned dangerous objects, probably due to an escaping/avoiding effect. Imagine the following situation: we see from far away a dangerous object/entity, for example a scorpio; given that it is far away, we have some time for action preparation. We immediately start escaping from it. When the scorpio is very close to us, instead, we are afraid, thus we stop and we avoid moving. Combining information on space and time, our results depict a situation similar to the one we have just described.
In the present study we simply presented dangerous and neutral objects, without introducing finer distinctions, for example between threatening and dangerous entities, even if the dynamic presentation suggested a potential threatening effect. Further research is needed to better understand how the motor responses to different kinds of dangerous entities occur in space and time.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
This work was supported by Grant from MIUR (PRIN 2008) and by the European Community, in FP7 project ROSSI: emergence of communication in robots through sensorimotor and social interaction (Grant agreement no: 216125). Part of this work was carried on with the support of the Marino Golinelli Foundation (Bologna, Italy). Many thanks to two reviewers for their helpful comments on a previous version of this manuscript.