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Context Effects on the Processing of Action-Relevant Object Features
Giovanna Girardi
University of Rome “La Sapienza”
Oliver Lindemann and Harold Bekkering
Radboud University Nijmegen
In 4 experiments, we investigated the effects of object affordance in reach-to-grasp actions. Participants
indicated whether a depicted small or large object was natural or manmade by means of different
object-grasping responses (i.e., with a power or a precision grip). We observed that the size of the
depicted object affected the grasping kinematics (grip aperture) and the reach-onset times of compatible
and incompatible actions. Additional experiments showed that the effect of perceived object size on
motor response was modulated by contextual action information and the observation of others’ actions
with the object. Thus, beyond the observation of object affordance effects in natural grasping actions, this
study suggests that the coupling between object perception and action is not static and obligatory.
Behavioral effects of action-relevant object features seem rather to depend on contextual action infor-
mation.
Keywords: object affordance, action context, object grasping, action observation, action intention
Over the past decade, cognitive science has shown increased
interest in understanding the relation between the functional pro-
cesses necessary to initiate a goal-directed action and the processes
essential for perception and thought. For example, compatibility
effects between object perception and motor response have been
shown to be bidirectional. That is, stimulus features can affect the
characteristics of potential actions (i.e., stimulus–response com-
patibility; e.g., Hommel, 1995; Kornblum, Hasbroucq, & Osman,
1990; Simon, 1969), and characteristics of a prepared or executed
action can influence the perception of stimulus features (i.e.,
response–stimulus compatibility; e.g., Craighero, Fadiga, Rizzo-
latti, & Umilta`, 1999; Fagioli, Ferlazzo, & Hommel, 2007; Fagioli,
Hommel, & Schubotz, 2007; Mu¨sseler & Hommel, 1997). Two
dominant theoretical views of the coupling between object percep-
tion and action can be distinguished: theories of direct perception
and theories of ideomotor action.
Theories of direct perception assume that perceptual processes
are intimately related to motor processes and claim that people
perceive each object in their environment in terms of potentially
afforded behaviors (e.g., Gibson, 1979). Gibson (1979) argued that
the affordances of objects are based on their intrinsic perceptual
properties, registered automatically and without the need for fur-
ther cognitive processes such as object recognition. To test this
notion, Tucker and Ellis (2001) required their participants to
indicate the semantic category of natural and manmade objects by
mimicking either a full or a precision handgrip. They found a
compatibility effect between the size (large or small) of the pre-
sented object and the required response (full or precision hand-
grip). They interpreted their findings as an object affordance effect
reflecting the directly perceived relation between certain visual
object properties and possible motor responses (see also Derby-
shire, Ellis, & Tucker, 2006; Ellis & Tucker, 2000; Ellis, Tucker,
Symes, & Vainio, 2007; Vainio, Symes, Ellis, Tucker, & Ottoboni,
2008).
Interestingly, Glover, Rosenbaum, Graham, and Dixon (2004)
demonstrated that interference effects between object properties
and motor responses are not only present for simple button-press
responses but can also be found in natural object– directed reach-
to-grasp movements. To be precise, they investigated the influence
of object words on the movement kinematics of grasping actions
and observed larger maximum grip apertures after reading words
representing relatively large objects (e.g., APPLE) than after read-
ing words representing relatively small objects (e.g., GRAPE). As
a more detailed analysis revealed, the object affordance effects in
word reading on grasping kinematics were already present very
early in the reach, suggesting that the effect of the object words
emerged during action planning and online motor control (see also
Glover, 2004). Taking into account the finding of automatic word-
reading effects, it seems plausible to assume that the processing of
visual object features (e.g., object size) also affects the kinematics
of natural reach-to-grasp actions. However, until now there has
been no behavioral evidence for such an impact of visual action-
related object information on grasping kinematics that went be-
yond response latency measurements and a facilitated execution of
compatible motor response.
The finding of object affordance effects on button-press laten-
cies has been interpreted as support for the idea that perceived
object affordances automatically and obligatorily affect the plan-
ning of subsequent motor responses. However, the notion that the
processing of visual object information takes place in an automatic
fashion does not imply that simply viewing graspable objects
automatically potentiates components of the actions they afford.
Giovanna Girardi, Department of Psychology, University of Rome “La
Sapienza”; Oliver Lindemann and Harold Bekkering, Donders Institute for
Brain, Cognition and Behavior, Radboud University Nijmegen.
We thank Gabriella Antonucci and Shirley-Ann Rueschemeyer for their
comments on earlier versions of the article. This research was supported by
the ICIS project sponsored by the Dutch Ministry of Economic Affairs
(Grant BSIK03024). Giovanna Girardi and Oliver Lindemann put an equal
amount of work into this project and therefore share first authorship.
Correspondence concerning this article should be addressed to Giovanna
Girardi, Department of Psychology, University of Rome “La Sapienza,” via
dei Marsi, no. 78, 00185 Rome, Italy. E-mail: giovanna.girardi@uniroma1.it
Journal of Experimental Psychology: © 2010 American Psychological Association
Human Perception and Performance
2010, Vol. 36, No. 2, 330–340
0096-1523/10/$12.00 DOI: 10.1037/a0017180
330
Empirical evidence for this is coming, for instance, from a study of
Tipper, Paul, and Hayes (2006), which recently demonstrated that
action affordance effects on grasping were larger when partici-
pants were presented with an active action state of the object, such
as a door handle depressed by 45%, than when they were presented
with the same object in a passive state (i.e., horizontal). According
to Tipper et al., this benefit of the active state suggests that the
activation of affordance from object perception is context depen-
dent and might be mediated by mental simulations of another
person’s action with the object. Moreover, Bub and Masson (2006)
have recently demonstrated that object affordance effects emerge
only if the observer attends to the object. Passive viewing without
the intention to act does not evoke hand gesture knowledge. Taken
together, recent observations have argued against the idea that
processing of action-related object features obligatorily activates
consistent action plans. That is, even though action-relevant infor-
mation is probably automatically extracted and processed and
object perception is not, this knowledge does not obligatorily
affect processes of action planning and execution. Rather, the
behavioral impact of perceived object affordance seems to depend
heavily on the action context in which the object is presented as
well as on the concurrent motor intentions of the observer.
Another approach to the coupling of perception and action is
provided by theories of ideomotor action, which basically hold that
movements are exhaustively coded in terms of their sensory con-
sequences (e.g., Greenwald, 1970), and by theories of common
coding, which assume that representations of perception and action
are based on the same cognitive codes and thus operate on the
same representational domain (Hommel, Mu¨sseler, Aschersleben,
& Prinz, 2001; Prinz, 1990). The central assumption shared by
both views is that motor actions and perceptual effects are highly
interrelated and mutually dependent. Experimental evidence for
this idea comes from studies on imitation showing that the per-
ception of a hand or finger movement facilitates the execution of
consistent motor actions (Bertenthal, Longo, & Kosobud, 2006;
Brass, Bekkering, & Prinz, 2001; Brass, Bekkering, Wohlschla¨ger,
& Prinz, 2000; Stu¨rmer, Aschersleben, & Prinz, 2000). For exam-
ple, Stu¨rmer et al. (2000) required participants to open or close
their hand in response to the color of a picture of an opening or
closing hand. Although the depicted action was irrelevant to the
assigned task, participants responded faster when they had to
execute the same action as that in the picture. Likewise, Brass et al.
(2001) demonstrated that people are faster in initiating a finger
movement to an arbitrary cue when an irrelevant but response-
compatible visual finger movement is shown simultaneously. To-
gether, the reports of automatic imitation effects show that per-
ceived sensory action consequences automatically activate the
representations of associated actions.
In contrast to the direct perception view, the common coding
approach predicts perceptual effects on action planning and as-
sumes a bidirectional connection between perception and ac-
tion—a notion that also implies the possibility of action-induced
effects on perception (Hommel et al., 2001). Because visual ob-
jects and motor actions are assumed to be represented by shared
features codes, it is expected that action planning affects percep-
tual processing by biasing the cognitive system toward feature
dimensions that are relevant for the preparation of the intended
response (Hommel et al., 2001). For instance, the intention to
grasp an object should prepare the visual system for the processing
of grasp-related object features. Such enhanced activation of codes
of features defined on motor-relevant dimensions can be under-
stood as a sort of intentional weighting process (see, e.g., Hommel,
in press). In fact, several studies have reported evidence for action-
induced effects and demonstrated that the preparation of a motor
response affects visual processing of objects and events that is
consistent with the currently intended action (Craighero et al.,
1999; Fagioli, Hommel, & Schubotz, 2007; Hamilton, Wolpert, &
Frith, 2004; Lindemann & Bekkering, 2009; Schubo¨, Prinz, &
Aschersleben, 2004; Wohlschla¨ger, 2000; Zwickel, Grosjean,
& Prinz, 2007). As one example, Craighero et al. (1999) demon-
strated that the processing of a visual stimulus is facilitated if it
affords the same type of grasping response as the participant
concurrently intends to perform. In their paradigm, participants
were instructed to prepare to grasp differently oriented wooden
bars but to delay the response execution until a visual go-signal
was presented. They observed faster detections of go-signals that
afforded the same type of grip as that involved in the prepared
action, indicating that the preparation of an object-directed motor
response facilitates the visual processing of action-consistent stim-
uli and showing that the intention to grasp an object is sufficient to
constitute an action context that modulates visual perceptual pro-
cessing.
Interestingly, as we know from recent research on the represen-
tation of functional object knowledge, the mere observation of a
grasping action or hand posture strongly influences semantic judg-
ments of graspable objects (Paulus, Lindemann, & Bekkering, in
press; Vainio et al., 2008; Yoon & Humphreys, 2005). Yoon and
Humphreys (2005), for instance, presented pictures of tools to-
gether with hands that were holding the objects in different ways
and showed that this contextual action information strongly influ-
enced the time taken to identify how the object is typically used.
Taking into account the view of the bidirectional perception–
action coupling and the finding that task-irrelevant action infor-
mation modulates the semantic processing of familiar objects, it
might be speculated that action-induced effects on the perceptual
processing of objects and their affordances might be influenced by
contextual action information associated with the grasp and type of
use. However, so far we do not know much about the role of
others’ actions on the representation of affordances and a possible
interplay between processes of action observation and object per-
ception.
The major aim of this research was therefore to study object
affordance effects in natural reach-to-grasp actions while focusing
on the role of the action context in the processing of object
affordances. In four experiments, we required participants to judge
the semantic category (i.e., natural or manmade) of presented
objects. In contrast to previous studies on stimulus–response com-
patibility effects in object perception (e.g., Tucker & Ellis, 2001),
we required participants to indicate their decisions by performing
different types of reach-to-grasp movements. The aim of the first
experiment was to determine whether the perception of visual
object properties interferes with the planning and execution of
natural grasping movements by investigating the effects of object
affordances on the reach onset times and movement kinematics of
grasping actions. In subsequent experiments, we applied this par-
adigm to examine effects of action context on object perception. In
particular, we focused on the role of the perception of another’s
action by examining the potential influence of action observation
331
ACTION CONTEXT AND OBJECT PERCEPTION
on the presence of the object affordance effect, that is, the com-
patibility effect between presented object and executed grasping
response.
Experiment 1
In Experiment 1, we examined the presence of object affordance
effects in natural grasping actions and moreover tested whether the
processing of action-related object features has an impact on both
components of a reach-to-grasp action, that is, on the reaching
(movement initiation times) and on the grasping (maximum grip
aperture [MGA]). To this end, we required participants to judge
the semantic category (natural or manmade) of a visually presented
object (fruit or tool) and to reach out for an object (manipulandum)
placed in front of them. More important, the decisions had to be
indicated by grasping the manipulandum with either a power grip
or a precision grip. We expected the time to initiate reaching to be
shorter when it was cued by an object affording the same type of
grip rather than a different type of grip, that is, an object affor-
dance effect (Tucker & Ellis, 2001). Taking into account previous
research showing an impact of semantic magnitude information on
grasping kinematics (Glover et al., 2004; Lindemann, Abolafia,
Girardi, & Bekkering, 2007; Lindemann, Stenneken, van Schie, &
Bekkering, 2006), we also expected the perceived object size to
affect the aperture of the hand during the reaching phase, as
revealed by an enlarged MGA for pictures of large as compared
with small objects.
Method
Participants. Twenty-one students of Radboud University
Nijmegen took part in the experiment in return for €4.50 ($6.39) or
course credit. All were right handed, had normal or corrected-to-
normal vision, and were naive with respect to the purpose of the
study.
Setup. In a dimly lit room, participants sat in front of a table
and were required to reach out for a wooden object (i.e., manipu-
landum). The manipulandum consisted of two parts: a large cyl-
inder (diameter ⫽6 cm, height ⫽7 cm) at the bottom and a small
cylinder (diameter ⫽0.7 cm, height ⫽1.5 cm) attached to top of
the large cylinder. It could be grasped in one of two ways: either
with a power grip at the large cylinder or with a precision grip at
the small cylinder (see Figure 1B). The manipulandum was placed
on the right side of the table behind an opaque screen (height ⫽44
cm, width ⫽45 cm), allowing participants to reach it comfortably
with their right hand without visual control (see Figure 1A). At a
distance of 30 cm from the center of the object, we fixated a small
pin (height ⫽0.5 cm, diameter ⫽0.5 cm) that served as a marker
for the starting position of the reach-to-grasp movements.
Stimuli. All stimuli were displayed on a gray background
using a 17-in. (43.2-cm) monitor (refresh rate ⫽100 Hz). Each
target stimulus consisted of a color photograph of a small or large
manipulable object. At a viewing distance of 50 cm, horizontal and
vertical visual angle ranged from about 3° (small objects such as a
paperclip) to 30° (a large object such as a saw). We used 20
manmade objects and 20 natural objects (see Appendix A for a list
of all objects). Half of the objects were small and consequently
afforded a precision grip action (e.g., a sharpener or a grape), and
the other half were large and required a power grip action (e.g., a
hammer or a banana).
1
Each object was depicted in two different
horizontal orientations. One orientation required a right-hand grasp
(e.g., handle on the right side), and the other required a left-hand
grasp (e.g., handle on the left side). Pictures of objects with
opposite alignments were obtained by mirroring the photographs.
Procedure. Before the experiment started, participants per-
formed a short preexperimental block in which they were required
to grasp the manipulandum with either a precision or a power grip,
depending on which colored dot was presented on the screen.
Specifically, they were required to reach out for the manipulandum
and to grasp it either at its large bottom part, using all of the fingers
on one hand (i.e., power grip response), or at its small top part,
using only their thumb and index finger (i.e., precision grip re-
sponse). The actual experiment started only when participants
were able to perform the grasping movements correctly and flu-
ently without vision.
At the beginning of each experimental trial, a gray fixation cross
was presented at the center of the screen; it indicated that partic-
ipants should place their index finger in the starting position. As
soon as their hand was placed correctly, the fixation cross turned
black and disappeared 1,500 ms later. After a random interval of
500 –2,000 ms, the target stimulus (i.e., tool or fruit) was pre-
sented. The participants’ task was to judge the semantic category
of the depicted object and to indicate their decision by performing
one of the two practiced actions (i.e., precision or power grip).
Responses had to be made as quickly and accurately as possible.
The target stimulus remained visible until the onset of reaching or
until 3,000 ms had elapsed. After performing the reach-to-grasp
movement, participants were required to grasp the object until the
gray fixation cross appeared to indicate the start of the next trial.
A stop sign, together with a beep sound (4400 Hz, lasting 200 ms),
1
Large and small objects were chosen considering the kind of grip
required to pick them up. We presented 56 pictures of manmade and
natural objects to 18 participants and asked them to indicate whether the
object required a precision or power grip to handle it appropriately. The 40
objects selected for the study were classified to a rate of 100% of the
responses as either a precision or a power grip object.
Precision Grip
Power Grip
B
A
Figure 1. Basic experimental setup. A: Participants sat at a table with a
computer screen and a manipulandum. An opaque screen blocked the view
of the manipulandum and the right hand. B: The manipulandum consisted
of two segments: a large cylinder at the bottom, affording a power grip, and
a small cylinder at the top, affording a precision grip.
332 GIRARDI, LINDEMANN, AND BEKKERING
was presented as error feedback if reach-to-grasp movements were
initiated before onset of the target stimulus.
Design. The mapping between the semantic object category
and the required response was counterbalanced between partici-
pants; that is, half of the participants performed a power grip action
in response to natural objects and a precision grip action in
response to manmade objects. For the other half, the stimulus–
response mapping was reversed. The experimental block consisted
of 160 trials (20 objects ⫻2 semantic categories ⫻2 object
orientations ⫻2 repetitions). All trials were presented in a ran-
domized order. In addition, at the beginning of the experiment we
presented 20 practice trials consisting of four sample objects
2
that
were not used in the experimental trials. The experiment lasted
about 45 min.
Data acquisition. To record the hand movements, we used an
electromagnetic position tracking system (miniBIRD 800TM, As-
cension Technology Corporation, Burlington, VT). Three sensors
were attached to the participants’ thumb, index finger, and right
wrist. Sensor positions were tracked at a sampling rate of 103 Hz.
The movement kinematics were analyzed offline. A fourth-order
Butterworth low-pass filter with a cutoff frequency of 10 Hz was
applied to the raw data. The onset of a reach-to-grasp movement
was defined as the first moment in time at which the tangential
velocity of the index finger sensor exceeded the threshold of 10
cm/s. For the offset, we used the opposite criterion, taking the time
of the first sample in which the velocity decreased below this
threshold.
As dependent variables for the statistical tests, we calculated the
mean response latencies of the reaching movements (response time
[RT], defined as the mean time elapsed between onset of picture
presentation and onset of reach-to-grasp movement), and the MGA
(defined as the maximum distance between the thumb and the
index finger during reaching) of the grasping. Anticipation re-
sponses (response before onset of go-picture presentation and
RTs ⬍100 ms), missing responses (no reactions and RTs ⬎1,000
ms), and incorrectly performed actions (e.g., incorrect grasping,
wrong type of grip, movement stopped while reaching) were
considered to be errors and excluded from further analyses. A
Type I error rate alpha of .05 was used in all statistical tests
reported here.
Results
The rate of anticipations (⬍1%) and errors (1.8%) was low,
showing that participants had carefully executed the object cate-
gorization task.
Reach onset latencies. We subjected the mean RTs to a
repeated measures analysis of variance (ANOVA) with object size
(large or small) and motor response (power grip or precision grip)
as within-subjects factors. The analysis revealed a significant main
effect of object size, F(1, 20) ⫽39.53, p⬍.001, indicating that
large objects were identified faster (469 ms) than small objects
(493 ms). There was a tendency for power grip responses to be
initiated faster (477 ms) than precision responses (485 ms), F(1,
20) ⫽3.37, p⫽.08. The two-way interaction between object size
and motor response was significant, F(1, 20) ⫽6.76, p⬍.02 (see
Figure 2). As revealed by post hoc t-test comparisons, when large
objects were presented, participants initiated power grip responses
(459 ms) faster than precision grip responses (479 ms), t(1, 19) ⫽
2.84, p⬍.001; when small objects were presented, RTs for the
precision grip responses (491 ms) were descriptively shorter than
for the power grip responses (496 ms). However, this contrast
failed to reach significance (t⬍1).
Grasping kinematics. We conducted a repeated measures
ANOVA with the factors object size (large or small) and object
category (natural or manmade) on the mean MGAs. The analysis
showed a main effect of object size, F(1, 20) ⫽4.58, p⬍.05. That
is, grip apertures were larger when grasping the manipulandum
while viewing large objects (109.7 mm) than while viewing small
objects (108.5 mm). Neither the main effect of object category nor
the interaction between the two factors reached significance (both
Fs⬍1).
Discussion
Experiment 1 demonstrates that reach-to-grasp movements are
affected by visual processing of objects affording different types of
actions. The object compatibility effect on the reach onset latencies
reflects that participants initiated power grip actions faster in
response to large objects (e.g., a hammer) than in response to small
objects (e.g., a sharpener). This finding provides the first direct
empirical support for the notion of object affordance effects in
complex natural grasping actions and thus extends previous find-
ings of object affordance effects on the execution of finger move-
ments that are involved in power or precision grip actions (Tucker
& Ellis, 2001). Moreover, we observed that the MGA was larger
while viewing a large object than while viewing a small object.
The object size effect in the grasping kinematics demonstrates an
impact of task-irrelevant magnitude information on motor behav-
ior, as has previously been reported for word-reading and number-
processing tasks (Glover et al., 2004; Lindemann et al., 2007), and
shows that similar effects also emerge during processing of visual
2
A cherry tomato, a tangerine, a carving fork, and a nail were used as
sample objects for the training trials.
Precision Grip Power Grip
430
440
450
460
470
480
490
500
510
520
530
Reaction Times (ms)
Small Objects
Large Objects
Figure 2. Mean response latencies of the grasping movements in Exper-
iment 1 as a function of the factors motor response and object size.
333
ACTION CONTEXT AND OBJECT PERCEPTION
information. The object affordance effect in the reach-onset laten-
cies was significant only for large objects. This dissociation be-
tween small and large objects was possibly driven by the fact that
small objects were more difficult for the participants to discrimi-
nate, and as a result, they were not strongly associated with a
particular motor representation. The idea of object affordances and
the observation of response compatibility effects in object percep-
tion has led many researchers to conclude that the processing and
representation of action-relevant visual information in object per-
ception takes place in a rather automatic way (see, e.g., Tucker &
Ellis, 2001). The finding of interference effects between object
perception and motor actions, however, does not inevitably imply
that the detection of action-relevant object features automatically
activates motor representations suited for manipulation of objects
(Phillips & Ward, 2002). Alternatively, it might be possible that
affordances are automatically processed but do not obligatorily
activate motor actions.
As mentioned in the introduction, ample evidence has shown
that the intention to perform a motor movement facilitates the
processing of action-related perceptual features such as object size
(Fagioli, Hommel, & Schubotz, 2007) or orientation (Craighero et
al., 1999) or the detection of action-consistent events (Lindemann
& Bekkering, 2009). It has therefore been argued that the activa-
tion of action representations has a direct impact on subsequent
attentional and perceptual processes by facilitating the processing
of action-relevant features and dimensions. Along the lines of this
intentional weighting hypothesis (see Hommel, in press), one
might also speculate that the mere observation of another person’s
object grasping modulates the processing of action-relevant object
features. If so, one might expect that object affordance effects
depend on concurrently activated representations of others’ motor
behavior and contextual information about others’ action inten-
tions. A possible means of testing this hypothesis is to manipulate
the action context, that is, the scenario in which the object is
perceived, and to investigate whether the presence of another
person’s grasping action affects the perceptual processing of
action-related object features and, thus, the activation of afforded
actions. We therefore conducted another experiment, the aim of
which was to examine the influence of contextual information on
the presence of object affordance effects.
Experiment 2
In Experiment 2, we investigated whether the action context in
which an object is perceived affects the presence of object affor-
dance effects on grasping responses. As in Experiment 1, partici-
pants were instructed to reach out and grasp the manipulandum
differently depending on the semantic decision task regarding the
nature of visually presented large and small objects. To investigate
the influence of observing another’s action on processing of object
affordances, we presented the objects in the context of different
grasping actions by also showing pictures of hands approaching
the object with either a power or a precision grip. Because the
depicted objects were either small or large, the grip size of pre-
sented hand postures was thus either appropriate or inappropriate
with respect to the action afforded by the object. Because of the
manipulation of observed hand– object relations, it was possible to
test whether object affordance effects are modulated by action
context.
As we know from previous research on ideomotor compatibility
effects (Brass et al., 2000, 2001; Stu¨rmer et al., 2000), the obser-
vation of hand postures or hand movements has a direct impact on
the motor system and facilitates the execution of congruent motor
actions. If object affordances also automatically potentiate com-
ponents of actions, the object compatibility effect on grasping
actions should not be mediated by contextual information. In this
case, we expect to find two independent but not interfering effects,
that is, an effect of the object’s affordance and an ideomotor effect
of the hand posture. If the processing of object affordances, how-
ever, is modulated by the action context, we expect that the effects
of object affordance on motor responses will be modulated by the
depicted hand posture and its relation to the required response.
Method
Participants. Twenty-four students of Radboud University
Nijmegen took part in the experiment. All were right handed, had
normal or corrected-to-normal vision, and were naive with respect
to the purpose of the study. They received €4.50 ($6.39) or course
credit for their participation.
Setup stimuli and data acquisition. The experimental setup
and the data acquisition were identical to those of Experiment 1. A
new set of color photographs of 20 small or large tools (i.e.,
manmade objects) and 20 small or large fruits (i.e., natural objects)
were used as target stimuli (see Appendix B for a list of all
objects). In contrast to previous studies, each object was always
presented along with a photograph of the left or right hand (see
Figure 3A). Each object subtended a visual angle of between 3°
(small objects such as a paperclip) and 25° (large objects such as
a teapot). The pictures of the hands (visual angle ⫽18°) were
presented randomly to the left or the right of the object. More
important, all stimuli were assembled in such a way that the
depicted hand appeared to approach the object. That is, right hands
were always shown to the left of the object and left hands to the
right. The left-hand picture was obtained by mirroring the photo-
graph of the right hand. For the no-go trials, the picture of the hand
was tinted blue.
Procedure. The procedure was basically identical to that of
Experiment 1. Participants indicated the semantic category of the
presented object (i.e., manmade or natural) by means of different
grasping responses (i.e., precision or power grip). To ensure that
participants paid attention to both object and hand, we introduced
additional no-go trials in which the hand was tinted blue. In these
trials, participants had to refrain from responding irrespective of
the object category.
Design. The mapping between the semantic object category
and the required response was again counterbalanced between
participants. The experimental block consisted of 160 randomized
experimental trials (20 objects ⫻2 semantic categories ⫻2
grasping postures ⫻2 object orientations) and 32 no-go trials.
Again, motor responses were trained in a short preexperimental
block. The experiment lasted about 45 min.
Because of the factorial combinations of the required grasping
responses and the two orthogonal stimulus features of object size
and depicted hand posture, each trial was compatible or incom-
patible with respect to object size and posture. That is, depending
334 GIRARDI, LINDEMANN, AND BEKKERING
on whether the grip was the same or different from that of the
hand in the photograph, a response could be considered as
posture compatible or incompatible. Moreover, each response
was, depending on whether the grip size matched the object
size, either object compatible or incompatible, as was the case
in Experiment 1.
Results
The low percentage of anticipations (⬍1%) and incorrectly
performed actions (3.0%) indicated that participants had per-
formed the task carefully.
We subjected the mean RTs to an ANOVA with the within-
subjects factors motor response (power grip or precision grip),
object compatibility (compatible or incompatible), and posture
compatibility (compatible or incompatible). The analysis revealed
a effect for the factor motor response, F(1, 23) ⫽6.98, p⬍.01,
showing that power grip responses (572 ms) were initiated faster
than precision grip responses (596 ms). Also, the main effect of
object compatibility reached significance, F(1, 23) ⫽9.39, p⬍
.01, indicating that grasping actions compatible with the action
afforded by the object (578 ms) were initiated faster than incom-
patible grasping actions (589 ms). There was no effect for the
factor posture compatibility, F(1, 23) ⫽1.6. More important,
however, there was a significant interaction between the factors
object compatibility and posture compatibility, F(1, 23) ⫽13.6,
p⬍.001 (see Figure 4). No other interaction of the ANOVA
reached significance (all Fs⬍1).
As post hoc t-test comparisons revealed, responses were faster
toward compatible objects only if the depicted posture was com-
patible with the required response (572 ms vs. 593 ms), t(23) ⫽
4.32, p⬍.001. For posture-incompatible trials, however, there
was no effect of object compatibility (585 ms vs. 586 ms; |t|⬍1).
Discussion
Experiment 2’s results show that object affordance effects were
present only if the depicted hand posture was compatible with the
required grasping action. That is, the execution of grasping was
facilitated only if both stimulus features (i.e., object size and hand
posture) were compatible with the response. However, in condi-
tions in which one or both stimulus features were incompatible,
RTs did not differ from one another. This finding clearly excludes
the possibility of two independent effects of object size and hand
posture; rather, it suggests that the effect of object affordance on
action execution depends on the concurrent action intention and
the relation between depicted hand posture and required motor
action. Experiment 2 shows consequently that ideomotor compat-
ibility effects between perceived and performed actions (Brass et
al., 2000) modulate the processing of action-related object features
and its impact on the motor system.
However, we cannot exclude at this point that the interaction
between object compatibility and posture compatibility originates
from interference at the perceptual stage of stimulus identification
and is not driven, as interpreted earlier, by stimulus–response
Figure 3. Examples of stimuli in Experiments 2, 3 (A), and 4 (B) for the two types of stimulus–response
compatibility— object and hand posture—in the case of a required power grip action. The side of hand
presentation (left or right) was counterbalanced. Note that because pointing actions were unrelated to hands
and objects, responses in Experiment 3 could not be classified as object or posture compatible (see text for
details).
Object Compatible Object Incompatible
560
570
580
590
600
610
620
630
640
650
660
Reaction Times (ms)
Posture Compatible
Posture Incompatible
Figure 4. Mean response latencies of the grasping movements in Exper-
iment 2 as a function of the factors object compatibility and posture
compatibility.
335
ACTION CONTEXT AND OBJECT PERCEPTION
relations. It might be possible that effects of object perception on
the grasping actions emerge only if the object is part of a mean-
ingful grasping action scenario in which the depicted hand posture
is shaped appropriately to grasp an object (i.e., a small object next
to a precision handgrip or a large object next to a power handgrip).
The observed interaction would in this case merely be the result of
facilitated processing of objects presented next to appropriately
shaped hands, which would reflect an effect of visual familiarity
based on people’s experiences in action observation. To control for
this alternative explanation, we conducted another experiment.
Experiment 3
In Experiment 3, we aimed to examine the origin of the inter-
action between posture and object compatibility in greater detail.
We tested in particular whether the interference effect observed in
Experiment 2 reflected an overlap between action stimulus and
response features (ideomotor stimulus–response compatibility) or
whether it was driven by an intrastimulus consistency of two
stimulus features, that is, the fit of the depicted grasping hand and
the object size (stimulus–stimulus congruency effect; see Korn-
blum et al., 1990). A straightforward way to disentangle these two
explanations is to minimize the ideomotor compatibility between
observed and executed actions. To do so, we modified the required
action responses and instructed participants to perform pointing
movements, which are, in contrast to the grasping actions in the
previous experiment, unrelated to the depicted hand postures. If
the observed interference effect in Experiment 2 reflects a facili-
tated perceptual processing of consistent action scenarios in which
the grip size of the presented hand posture fits the object size, RT
effects should be independent of the required type of motor re-
sponse and thus also be present for pointing movements. On the
contrary, no difference should be expected in pointing latencies if
the observed effects depend on the compatibility between the
selected responses and the depicted action scenarios.
Method
Participants. Twenty-four right-handed students of Radboud
University Nijmegen took part in the experiment in return for
€4.50 ($6.39) or course credit. All had normal or corrected-to-
normal vision and were naive with respect to the purpose of the
study.
Setup, stimuli, and procedure. The experimental setup, stim-
uli, and procedure were almost identical to those of Experiment 2.
The only modification was that participants had to indicate their
judgments by pointing movements. That is, depending on the
semantic category of the depicted object, participants were re-
quired to point either to the small top or to the large bottom part of
the manipulandum. The actions were executed in a training phase
until participants attained sufficient expertise. Half of the partici-
pants pointed to the small top cylinder when viewing a natural
object and to the large bottom cylinder when viewing a manmade
object. The response mapping was reversed for the other partici-
pants.
Data acquisition and design. The data acquisition and exper-
imental design were identical to those of Experiment 3. Because
pointing actions were not related to the hands and objects, re-
sponses could not be classified as object or posture compatibility.
We therefore analyzed the latencies with respect to possible intra-
stimulus effects of the congruency between the depicted hand
posture and the size of the object (i.e., stimulus congruency).
Results
The anticipation rate was less than 1%; incorrectly performed
actions occurred in only 2.2% of the trials. A repeated measures
two-way ANOVA on the mean RTs revealed no main effect for the
factors stimulus congruency (congruent or incongruent), F(1,
23) ⫽2.03, p⬎.1, and motor response (pointing to the bottom or
pointing to the top), F(1, 23) ⫽3.07, p⬎.05. Also, the interaction
between the two factors failed to reach significance (F⬍1). This
finding suggests that semantic judgments and motor responses
were not facilitated for stimuli in which the grip size of the
depicted hand posture fit the object (667 ms) as compared with
incongruent stimuli (674 ms).
To compare the congruency effects for grasping (Experiment 2)
and pointing actions (Experiment 3) directly, we performed a
mixed ANOVA with the between-subjects factor experiment and
the within-subjects factor stimulus congruency. As the significant
interaction between the two factors confirmed, F(1, 46) ⫽3.90,
p⫽.05, stimulus consistency effects were present only in Exper-
iment 2, t(23) ⫽5.05, p⬍.001, and not in Experiment 3, t(23) ⫽
1.42, p⬎.15. Furthermore, RTs in Experiment 3 were on average
slower (671 ms) than RTs in Experiment 2 (585 ms), F(1, 46) ⫽
10.80, p⬍.01. It might consequently be possible that stimulus
congruency effects emerge only if RT intervals are relatively short
and vanishing congruency effects were thus the result of an overall
RT difference. To exclude this possibility, we performed a RT
distribution analysis and investigated the time course of a possible
stimulus congruency effect in Experiment 3 (see Ratcliff, 1979).
RTs for motor response and stimulus congruency conditions of
each participant were rank ordered, divided into quintiles, aver-
aged, and submitted to a repeated measures ANOVA. The inter-
action between the factors stimulus congruency and quintiles
(F⬍1) failed to reach significance, indicating an absence of
stimulus congruency effects for the slow and the fast responses.
We can therefore exclude that the vanishing of the congruency
effect was the result of the overall RT difference between Exper-
iments 2 and 3.
Discussion
When participants performed pointing movements, we observed
no congruency effect between depicted object and depicted hand
postures. This finding argues against the possibility that the out-
come of Experiment 2 was driven by stimulus–stimulus congru-
ency effect, that is, a facilitated perceptual processing of congruent
action scenarios in which the grip size of the presented hand
posture fitted the size of the object. We can therefore exclude that
the modulation of object affordance effects by observed hand
postures had a mere perceptual origin.
Our experiments demonstrate that the compatibility between
observed and performed grasping actions modulates the perception
and the cognitive effects of the object affordances. Interestingly,
Experiment 2 revealed no main effect for the factor posture com-
patibility, that is, faster initiations of grasping responses consistent
336 GIRARDI, LINDEMANN, AND BEKKERING
with the depicted hand postures. At first glance, this finding might
be unexpected because several previous studies have reported the
presence of ideomotor compatibility effects for motor response
that are consistent with observed hand movements (Brass et al.,
2000; Stu¨rmer et al., 2000; but see also Vainio, Tucker, & Ellis,
2007). In contrast to these studies, the hands in Experiment 2’s
pictures were never presented alone without an object. Neverthe-
less, we can exclude that they were not processed because hand
posture compatibility modulated the presence of object affordance
effects. The lack of an ideomotor compatibility effect can be
interpreted as an indication that participants processed the hand
and the object as one integrated action scenario and not as two
separate stimuli. Alternatively, the dominance of object affordance
effects might be because the semantic categorization task required
participants to focus their attention on the object and less on the
depicted hand. This raises the question of whether both hand
posture compatibility and object affordance effects emerge simul-
taneously while viewing an object and a hand that are not per-
ceived as two related entries. In Experiment 4, therefore, we tested
whether two independent stimulus–response compatibility effects
for object and hand can be observed if they are presented as
spatially separated visual stimuli that are not part of one action
context.
Experiment 4
Experiment 4 investigated the presence of stimulus–response
compatibility effects of the depicted object and hand posture under
conditions in which they are not elements of one integrated object-
directed action. The same pictures were presented as in the previ-
ous experiments. However, objects and hand postures were now
presented at two separate locations on the screen so that they did
not appear to be two related elements in one grasping action
scenario. We expected that if objects and hands are perceived as
two separate stimuli, RTs would reflect two independent effects,
that is, an effect of the object affordance and an effect of ideomotor
compatibility.
Method
Participants. Twenty-four right-handed students of Radboud
University Nijmegen took part in the experiment in return for
€4.50 ($6.39) or course credit. All had normal or corrected-to-
normal vision and were naive with respect to the purpose of the
study. None of the students had participated in the other experi-
ments.
Setup, stimuli, and procedure. The experimental setup, stim-
uli, and procedure were basically the same as in Experiment 2. The
only modification was the arrangement of the hand and object
stimuli on the screen. Instead of presenting the two pictures in
spatial proximity to one another, object and hand posture were
presented in the left and right visual field (4° eccentricity), respec-
tively, so that the hand did not appear to approach the object (see
Figure 3B). As in Experiments 2 and 3, the pictures of right hands
were presented to the left of the object and left hands were
presented to the right.
Data acquisition and design. The data acquisition and exper-
imental design were identical to those of Experiment 2.
Results
The rate of anticipations was less than 1%. The error rate was
5.2%. The three-way repeated measures ANOVA (Motor Re-
sponse ⫻Object Compatibility ⫻Posture Compatibility) of the
mean RTs revealed significant effects for both compatibility fac-
tors. Object-compatible responses (627 ms) were initiated faster
than object-incompatible responses (648 ms), F(1, 23) ⫽23.85,
p⬍.001, and responses compatible with the depicted posture (633
ms) were initiated faster than the posture-incompatible responses
(641 ms), F(1, 23) ⫽3.95, p⬍.05 (see Figure 5). Interestingly,
the interaction of the two compatibility factors did not reach
significance, F(1, 23) ⫽1.2, indicating that the effects of object
and of posture compatibility occurred independently of one an-
other and did not interfere.
Again, participants showed a tendency to initiate power grip
responses (629 ms) faster than precision grip responses (645 ms),
F(1, 23) ⫽3.83, p⬍.07. The two-way interactions between motor
response and object compatibility and between motor response and
posture compatibility were both significant, F(1, 23) ⫽9.39, p⬍
.005, and F(1, 23) ⫽11.46, p⬍.003, respectively. These inter-
action effects indicate that both object and posture compatibility
effects were larger for power grip responses (34 ms and 19 ms,
respectively) than for precision grip responses (8 ms and 3 ms,
respectively), ts(23) ⫽3.32 and 2.94, ps⬍.05.
To test whether the influence of the depicted hand posture on the
object compatibility effect was different in Experiment 4 than in
Experiment 2, in which object and hand posture were presented
close together, we performed a between-experiments comparison.
To this aim, we calculated the size of the object compatibility
effects, defined as the RT difference between object-incompatible
and object-compatible trials, for each participant in both experi-
ments. We entered the resulting RT effects into a mixed design
ANOVA with the between-subjects factor experiment (Experiment
2 or Experiment 4) and the within-subject factor posture compat-
ibility. Besides the main effect of posture compatibility, F(1, 46) ⫽
Object Compatible Object Incompatible
560
570
580
590
600
610
620
630
640
650
660
Reaction Times (ms)
Posture Compatible
Posture Incompatible
Figure 5. Mean response latencies of the grasping movements in Exper-
iment 4 as a function of the factors object compatibility and posture
compatibility.
337
ACTION CONTEXT AND OBJECT PERCEPTION
11.49, p⬍.001, the analysis yielded a significant interaction
between the two factors, F(1, 46) ⫽4.34, p⬍.05. Post hoc ttests
showed that the depicted hand postures had an impact on the
presence of the object compatibility effect only in Experiment 2
(object compatibility effect for hand-compatible trials, 21.4 ms; for
hand-incompatible trials, 0.31 ms), t(23) ⫽3.68, p⬍.001, but not
in Experiment 4 (18.3 ms vs. 23.4 ms), t(23) ⬍1.
Discussion
Experiment 4 demonstrates the presence of two independent
stimulus–response compatibility effects, object affordance and
hand posture, if both were presented simultaneously but as two
separate stimuli. That is, grasping actions were initiated faster in
response to pictures of objects affording a compatible grip and in
response to pictures of compatible hand postures. More important,
the results revealed that the stimulus–response compatibility effect
of object and posture did not interact if the pictures were not
arranged so that the hand appeared to approach the object. The lack
of cross-talk under these circumstances shows that the relation
between the hand posture and the object modulates the presence of
object compatibility effects. As the comparison of the object
compatibility effects in Experiments 2 and 4 confirmed, the per-
ceptual processing of the object and hand posture interacted only
if they were perceived as two integrated parts of one action
scenario. This outcome points to the important role of the action
context in object perception and the processing of object affor-
dances.
General Discussion
Four experiments explored the cognitive interference between
perception and action and investigated, in particular, the role of
contextual information on the behavioral effects of perceived ob-
ject affordances. As the analyses of stimulus–response compati-
bility effects revealed, perceived affordances of an object had an
influence on the planning and execution of natural reach-to-grasp
actions. This observation is in line with several previous studies
showing that the perception of an object activates representations
of motor actions that are best suited for a manipulation of the
object (Glover et al., 2004; Phillips & Ward, 2002; Tucker & Ellis,
2001). More important, this study aimed to investigate the influ-
ence of the action context, that is, the influence of observation of
others’ actions on the processing of action-relevant object features.
It thus extends the literature on object perception and action
affordances in at least two aspects.
First, we demonstrated that the object affordance effects on
motor response are modulated by the action context in which the
object is perceived. We only found stimulus–response compatibil-
ity effects between object features and required motor responses
when the object was presented close to the hand grasping posture
so that they formed a meaningful grasping action (Experiment 2).
We did not, however find effects of the object affordance if an
object-inconsistent hand posture was presented. This interaction
shows that object affordance effects strongly depend on the action
context, that is, the observed action that is performed with the
object, suggesting that object-related actions are not automatically
activated in the observer. Interestingly, the compatibility effects
could not be observed when participants executed finger-pointing
movements (Experiment 3). We can consequently reject the alter-
native account of the outcome of Experiment 2 as a stimulus–
stimulus congruency effect and exclude the possibility that object
affordance effects were driven by a facilitated perceptual process-
ing of congruent action scenarios in which the grip size of the
presented posture fitted the size of the object. We therefore inter-
pret the dependence of the object affordance effect on the depicted
hand posture as evidence for an influence of contextual informa-
tion on object processing. This outcome is in line with other
studies showing that the associated functional object knowledge
becomes activated only if people intend to use the object with that
specific purpose (Bub & Masson, 2006; Lindemann et al., 2006) or
if the object is perceived in an active action context (Tipper et al.,
2006). We thence conclude that the activation of action represen-
tations and motor codes is not completely automatic and obligatory
(see, e.g., Tucker & Ellis, 2001).
Second, this study is among the first to demonstrate the
presence of object affordance effects in reaching and grasping
components of natural object-directed grasping actions. So far,
object affordance effects have mostly been reported only for
button-press responses or simple finger movements that are
involved in grasping actions (e.g., Derbyshire et al., 2006; Ellis
& Tucker, 2000; Tucker & Ellis, 2001). The major advantage to
using natural object-directed grasping action is the possibility
of dissociating between effects in reaching and grasping com-
ponents of motor response. Interestingly, object affordance
effects were evident in both the onset of the reaching move-
ments and the movement kinematics of the grasping. The effect
in the movement latencies shows, in line with motor theories
(Rosenbaum, Meulenbroek, Vaughan, & Jansen, 2001), that the
intended grip size at the end of the movement is anticipated and
planned before the hand has reached the target object. This
interference between object perception and action intention
clearly demonstrates that object affordance effects emerge at
the level of motor planning. Also, the finding of an enlarged
MGA indicates an interaction between object perception and
action planning. The effect on the grasping kinematics, more-
over, parallels research demonstrating effects of size-related
semantic information on grasping actions (Gentilucci, Benuzzi,
Bertolani, Daprati, & Gangitano, 2000; Glover et al., 2004;
Lindemann et al., 2007). Glover et al. (2004) have shown that
the modulation of the grip aperture by magnitude information
reflects interference at the level of action planning. The kine-
matics effect in this study consistently provided additional
support for our notion that the perception of action-relevant
object features interferes only with action planning but not with
motor control.
As mentioned before, the ideomotor theory suggests that
action representations are activated when observing visual
events that correspond to effects of own and others’ motor
actions (Hommel et al., 2001). With this study, we provide new
support for this view by demonstrating that ideomotor compat-
ibility effects are not restricted to simple finger movements and
also emerge in connection with complex action scenarios and
goal-directed reach-to-grasp movements. When the object and
the hand grasping posture were presented far away from one
another (Experiment 4), we found two effects. Observing a
grasping hand facilitates the execution of similar grasping ac-
tions (i.e., ideomotor compatibility effect; Brass et al., 2000;
338 GIRARDI, LINDEMANN, AND BEKKERING
Stu¨rmer et al., 2000), whereas observing a manipulable object
primes the execution of the grasping action associated with it
(cf. Tucker & Ellis, 2001). Interestingly, the behavioral effects
of object perception and action observation have mostly been
investigated in isolation. As this study now shows, object
affordance and ideomotor compatibility effects can arise under
certain conditions independently and do not necessarily inter-
fere. This independence indicates that the mere perception of
others’ actions is not sufficient to modulate the processing of
action-relevant object features and suggests that object and
action observation interact only if both aspects are conceived as
part of one meaningful action scenario (Experiment 2).
Taken together, these data argue against the view that visual
objects automatically and obligatorily potentiate components of
action they afford and rather provide evidence for the notion
that the processing of action-relevant object features depends
greatly on the contextual correspondence of perception and
action. The finding that object affordance effects depend on the
action context in which the object is perceived supports the idea
of an intentional weighting of action-relevant dimensions in
perceptual processing.
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Appendix A
Natural and Manmade Objects Presented in
Experiment 1
Small objects affording a precision grip action: almond, brussels
sprout, cranberry, garlic, grape, mushroom, nut, pepper, radish,
string bean, clothespin, key, lighter, paperclip, pen, pencil, sharp-
ener, screw, teaspoon, tweezers.
Large objects affording a power grip action: avocado, banana, carrot,
cucumber, eggplant, leek, mango, pear, paprika, potato, brush, corkscrew,
cup, hairbrush, hairdryer, hammer, knife, rake, saw, screwdriver.
Appendix B
Natural and Manmade Objects Presented in
Experiments 2, 3, and 4
Small objects affording a precision grip action: almond,
brussels sprout, cranberry, garlic, grape, mushroom, nut,
pepper, radish, string bean, chess piece, clothespin, dart,
hairspray, needle, paperclip, pushpin, sharpener, teaspoon,
tweezers.
Large objects affording a power grip action: avocado, banana,
carrot, cucumber, eggplant, leek, mango, pear, paprika, potato,
book, bottle, cup, iron, joystick, key, soft drink can, tea box,
teapot, thermos.
Received May 9, 2008
Revision received June 16, 2009
Accepted June 19, 2009 䡲
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340 GIRARDI, LINDEMANN, AND BEKKERING
