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RESEARCH ARTICLE The bottle and the glass say to me: ‘‘Pour!’’ Elisa De Stefani Alessandro Innocenti Nicolo ` Francesco Bernardi Giovanna Cristina Campione Maurizio Gentilucci Received: 10 November 2011 / Accepted: 21 February 2012 / Published online: 13 March 2012 Ó Springer-Verlag 2012 Abstract The present study aimed at determining whe- ther the observation of two functionally compatible arte- facts, that is which potentially concur in achieving a specific function, automatically activates a motor pro- gramme of interaction between the two objects. To this purpose, an interference paradigm was used during which an artefact (a bottle filled with orange juice), target of a reaching-grasping and lifting sequence, was presented alone or with a non-target object (distractor) of the same or different semantic category and functionally compatible or not. In experiment 1, the bottle was presented alone or with an artefact (a sphere), or a natural (an apple) distractor. In experiment 2, the bottle was presented with either the apple or a glass (an artefact) filled with orange juice, whereas in experiment 3, either an empty or a filled glass was pre- sented. In the control experiment 4, we compared the kinematics of reaching-grasping and pouring with those of reaching-grasping and lifting. The kinematics of reach, grasp and lift was affected by distractor presentation. However, no difference was observed between two dis- tractors that belonged to different semantic categories. In contrast, the presence of the empty rather filled glass affected the kinematics of the actual grasp. This suggests that an actually functional compatibility between target (the bottle) and distractor (the empty glass) was necessary to activate automatically a programme of interaction (i.e. pouring) between the two artefacts. This programme affected the programme actually executed (i.e. lifting). The results of the present study indicate that, in addition to affordances related to intrinsic object properties, ‘‘working affordances’’ related to a specific use of an artefact with another object can be activated on the basis of functional compatibility. Keywords Affordance Á Interference Á Human kinematics Á Semantic category Á Artefact Introduction Grasping an object requires the selection of a particular type of grasp. In addition, when the hand approaches the target (i.e. during reaching), the fingers are shaped and, then, closed on the object. Kinematic studies (Chieffi and Gentilucci 1993; Gentilucci et al. 1991, 1994; Jeannerod 1988; Milner and Goodale 1995) have shown that intrinsic object properties, such as size and shape, influence both the selection of the type of grasp and the grasp kinematics, whereas extrinsic properties, such as position, influence the reach kinematics. All these properties elicit affordances of the object. According to Gibson (1979), affordances are possibilities for action provided by means of vision. The idea of affordances would include, in the representation of an object, a description of its visual properties and the motor pattern required to interact with that object (see Jeannerod 1994; Ellis and Tucker 2000; see also Ellis et al. 2007). In this sense, affordances are also motor E. De Stefani Á A. Innocenti Á N. F. Bernardi Á G. C. Campione Á M. Gentilucci (&) Department of Neuroscience, University of Parma, Via Volturno 39, 43100 Parma, Italy e-mail: [email protected] N. F. Bernardi Department of Psychology, University of Milano-Bicocca, Milan, Italy M. Gentilucci RTM (Rete Multidisciplinare Tecnologica), IIT (Istituto Italiano di Tecnologia), University of Parma, Milan, Italy 123 Exp Brain Res (2012) 218:539–549 DOI 10.1007/s00221-012-3047-2
Transcript

RESEARCH ARTICLE

The bottle and the glass say to me: ‘‘Pour!’’

Elisa De Stefani • Alessandro Innocenti •

Nicolo Francesco Bernardi • Giovanna Cristina Campione •

Maurizio Gentilucci

Received: 10 November 2011 / Accepted: 21 February 2012 / Published online: 13 March 2012

� Springer-Verlag 2012

Abstract The present study aimed at determining whe-

ther the observation of two functionally compatible arte-

facts, that is which potentially concur in achieving a

specific function, automatically activates a motor pro-

gramme of interaction between the two objects. To this

purpose, an interference paradigm was used during which

an artefact (a bottle filled with orange juice), target of a

reaching-grasping and lifting sequence, was presented

alone or with a non-target object (distractor) of the same or

different semantic category and functionally compatible or

not. In experiment 1, the bottle was presented alone or with

an artefact (a sphere), or a natural (an apple) distractor. In

experiment 2, the bottle was presented with either the apple

or a glass (an artefact) filled with orange juice, whereas in

experiment 3, either an empty or a filled glass was pre-

sented. In the control experiment 4, we compared the

kinematics of reaching-grasping and pouring with those of

reaching-grasping and lifting. The kinematics of reach,

grasp and lift was affected by distractor presentation.

However, no difference was observed between two dis-

tractors that belonged to different semantic categories. In

contrast, the presence of the empty rather filled glass

affected the kinematics of the actual grasp. This suggests

that an actually functional compatibility between target

(the bottle) and distractor (the empty glass) was necessary

to activate automatically a programme of interaction (i.e.

pouring) between the two artefacts. This programme

affected the programme actually executed (i.e. lifting). The

results of the present study indicate that, in addition to

affordances related to intrinsic object properties, ‘‘working

affordances’’ related to a specific use of an artefact with

another object can be activated on the basis of functional

compatibility.

Keywords Affordance � Interference �Human kinematics � Semantic category � Artefact

Introduction

Grasping an object requires the selection of a particular

type of grasp. In addition, when the hand approaches the

target (i.e. during reaching), the fingers are shaped and,

then, closed on the object. Kinematic studies (Chieffi and

Gentilucci 1993; Gentilucci et al. 1991, 1994; Jeannerod

1988; Milner and Goodale 1995) have shown that intrinsic

object properties, such as size and shape, influence both the

selection of the type of grasp and the grasp kinematics,

whereas extrinsic properties, such as position, influence the

reach kinematics. All these properties elicit affordances of

the object. According to Gibson (1979), affordances are

possibilities for action provided by means of vision. The

idea of affordances would include, in the representation of

an object, a description of its visual properties and the

motor pattern required to interact with that object (see

Jeannerod 1994; Ellis and Tucker 2000; see also Ellis et al.

2007). In this sense, affordances are also motor

E. De Stefani � A. Innocenti � N. F. Bernardi �G. C. Campione � M. Gentilucci (&)

Department of Neuroscience, University of Parma,

Via Volturno 39, 43100 Parma, Italy

e-mail: [email protected]

N. F. Bernardi

Department of Psychology, University of Milano-Bicocca,

Milan, Italy

M. Gentilucci

RTM (Rete Multidisciplinare Tecnologica), IIT (Istituto Italiano

di Tecnologia), University of Parma, Milan, Italy

123

Exp Brain Res (2012) 218:539–549

DOI 10.1007/s00221-012-3047-2

representations of interactions between effector and object

(Barbieri et al. 2007; Gangitano et al. 1998; Gentilucci

2002, 2003). In kinematic studies of arm movements like

reaching and grasping, the affordances were studied using

interference paradigms, in which the target was presented

alone or with a distractor (i.e. an object irrelevant to the

motor task). Usually, the intrinsic properties of the dis-

tractor were different from those of the target (Castiello

et al. 1996; Gangitano et al. 1998). It was observed that the

different grasp motor patterns automatically activated by

the vision of the distractor (i.e. the distractor affordance)

influenced the actual grasp directed to the target. Tipper

and colleagues (Tipper et al. 1991, 1997; Howard and

Tipper 1997) observed that when individuals reached for a

target, their hand movements veered away from distractors

even if they were not physical obstacles to the action.

Similar effects were also found in tasks requiring saccadic

eye movements. When a cue was presented on the right or

on the left of fixation, the next saccades deviated away

from the locus of the cue (Sheliga et al. 1994, 1995). As

Tipper et al. (1991), Sheliga et al. (1994, 1995) interpreted

these path deviations as possible reflections of inhibition

related to the to-be-ignored cue stimulus. In other experi-

ments (Tresilian 1998; Mon-Williams and McIntosh 2000;

Mon-Williams et al. 2001), the presence of a distractor

slowed down the movement approaching the target and

induced a decrease in maximal finger aperture of grasp.

Mon-Williams et al. (2001) and Tresilian (1998) inter-

preted these results as consequent to the strategy for

decreasing the possibility of the fingers colliding with non-

target objects in the workspace. Alternatively, these results

could be due to interference of the programme directed to

the distractor not yet inhibited during movement execution.

Many cognitive models assumed that semantic memory

is organized in categories (Capitani et al. 2003). In partic-

ular, two main semantic categories have been identified: the

category of natural or biological objects (such as animals,

fruits and vegetables) and the category of artefacts or man-

made objects (such as tools) (Atran 1989; Farah et al. 1996;

Warrington and McCarthy 1987). Natural things can be

defined in terms of their sensory or perceptual properties. In

contrast, artefacts tend to be defined in terms of their

functional attributes (i.e. what they are used for) (Sensory

Functional Theory; Warrington and Shallice 1984). Con-

sequently, when used as distractors, natural things would

interfere with the actual action towards the target on the

basis of motor programmes (i.e. affordances) usually related

to their physical properties, whereas artefacts would also

compete on the basis of their motor programmes defined by

functional motor properties (Farah and McClelland 1991).

Affordances of artefacts can be, therefore, expressed in

terms of motor programmes describing the functions of the

object (beside programmes of interactions such as the grasp

on the basis of extrinsic and intrinsic tool properties, Borghi

et al. 2007; Costantini et al. 2011). Thereby, it is possible to

suppose that, when two artefacts (target and distractor) are

both presented on a scene, the distractor could activate a

motor programme ‘‘per se’’, that is, a structural affordance

determined by current information on physical properties of

the only distractor and/or a motor programme arising from

the combined use of the target with the distractor, that is, a

functional affordance based on stored knowledge of object

use (Bub et al. 2003, 2008; Creem-Regehr et al. 2007; Jax

and Buxbaum 2010). According to Riddoch and Humph-

reys’ group (Riddoch et al. 2003; Yoon et al. 2010), the

functional affordances are involved in detecting objects

presented within pairs. We hypothesized that the presenta-

tion of two artefacts normally associated with the same

action (e.g. a full bottle, the target, and an empty glass to be

filled, the distractor) can activate a specific programme (i.e.

of pouring), which interferes with the action on the target,

even if the task does not require the use of the target with the

distractor (e.g. reaching, grasping and lifting the bottle).

In experiment 1, participants reached, grasped a bottle

(an artefact) and lifted it. The target object was presented

alone or with non-target objects. These were a sphere or an

apple of the same sizes. The apple belongs to the natural

category (Atran 1989; Farah et al. 1996, 1991; Warrington

and McCarthy 1987), that is, a category different from that

of bottle. In contrast, the sphere was of the same category

as the bottle because it was an artefact, but functionally

unrelated with it. In sum, the presence of the sphere such as

the apple unlikely activates a programme of interaction

with the bottle. Consequently, concerning the functional

relations with the bottle, we expected no difference in the

interference between sphere and apple. It may be noted that

the natural object (the apple) placed on a table was not

presented in a natural background (i.e. the tree) even if it

was on a usual background (i.e. the table). Conversely, the

sphere was a wood graspable object that could be used as a

bowl. However, its presentation with a bottle in a table

plane is less frequent than presentation of apple with bottle.

That is, what are called thematic spatial relationships were

weaker. Consequently, concerning the thematic spatial

relations with the bottle, we might expect less interference

effect than the apple. Note that thematic relations corre-

spond to an organization of knowledge in terms of familiar

scenes or events and they affect the way categories are

formed and used. More specifically, a thematic relation is

any temporal, spatial, causal or functional relation between

things (Estes et al. 2011), and they can arise from either

affordances or convention (Golonka and Estes 2009; Lin

and Murphy 2001). A typical relation is spatial (e.g. a roof

on top of a house), but thematic relations could be also

temporal (e.g. summer and holiday), causal (e.g. wind and

erosion), and functional (e.g. fork and knife).

540 Exp Brain Res (2012) 218:539–549

123

In experiment 2, the interference effect of the apple with

that of a filled glass was compared. The glass is semantically

compatible with the bottle because it is an artefact and it is

also associated with one dominant function (it is used to drink

if it is filled with the liquid of the bottle, see Jax and Buxbaum

2010). Nevertheless, actually the full glass was not func-

tionally compatible with the bottle since it was already filled

with liquid. Consequently, we expected no difference

between the presentation of the apple and the filled glass. In

experiment 3, we compared the effect of the filled glass with

that of an empty glass. We expected an effect of the empty

glass; indeed, actually, the empty glass was functionally

compatible with the bottle. In other words, its presentation

could automatically activate a programme of pouring the

liquid of the bottle into the glass modifying the actual motor

programme. Indeed, a previous study (Ansuini et al. 2008)

showed that the kinematics of grasp differed when reaching to

grasp in order to lift as compared to pour. In other words, the

final action and/or its aim can affect the kinematics of an

entire sequence of actions (see also Gentilucci et al. 1997;

Marteniuk et al. 1987). Finally, experiment 4 was a control

aiming at confirming the kinematic differences between

motor sequences finalized to pour and to lift.

Experiment 1

In experiment 1, we examined whether in a task requiring

reaching, grasping and lifting a bottle (an artefact object),

the presence of a distractor of the same semantic category

could affect the sequence in a different way with respect to

a distractor of a different semantic category. We presented

the target alone, or in the presence of a distractor of the

same category (a sphere, artefact) or in the presence of a

distractor of a different category (an apple, natural object).

Methods

Participants

Eight naıve volunteers (5 women and 3 men, age

22–30 years.) took part in the experiment. All participants

were right-handed (Oldfield 1971) and without any history

of neurological disorder or impairment. They were paid for

their participation. The Ethics Committee of the Medical

Faculty at the University of Parma approved the study. The

experiments were conducted according to the principles

expressed in the Declaration of Helsinki.

Apparatus and stimuli

The participants sat comfortably in front of a table on

which they placed their right hand with the thumb and

index finger in pinch position (Starting Position, SP). SP

was along the participants’ mid-sagittal plane and was

27 cm distant from their chest. A bottle filled with orange

juice (*22 cm height, *5 cm diameter; Fig. 1) was pre-

sented to the participants. It was positioned on the table

along the participants’ mid-sagittal plane, 19 cm distant

from SP. The bottle was presented alone or, depending

upon the task condition, in the presence of another object

on the left, 15 cm distant from the bottle. The distance of

this object from the participants’ horizontal plane was the

same as that of the bottle (Fig. 1). The object could be a

yellow apple or a graspable wood sphere or another iden-

tical bottle filled with orange juice. The apple and the

sphere were approximately of the same size (apple: *7 cm

width, *8 cm height; sphere: *8 cm diameter; Fig. 1).

Procedure

The participants performed a go–no-go task. They were

required to reach for, pick up and lift the bottle in the

presence of the apple or the sphere (distractor condition) or

in the absence of any object (no-distractor condition). Each

trial started with the participant’s eyes closed. When the

experimenter gave the ‘‘GO’’ signal, the participant opened

his/her eyes, looked at the presented stimuli and then

reached, grasped and lifted the bottle (go condition). No

instruction was given about the height of the lifting move-

ment. The participants grasped the bottle with their whole

right hand (whole hand grasp, Fig. 1). When the second

bottle was presented on the table, the participants had to

stay still and to wait for the next trial (no-go condition).

Before the experiment onset, the participants performed a

training block of ten trials. The task was executed in a single

block of 40 trials (10 trials/condition) and the order of

stimulus presentation was semi-randomized. During the

task, the participants were free to look at the scene as during

natural interactions with objects and they were asked to

perform the movement as naturally as possible.

Data recording

The movements of the participants’ right arm were recorded

using the 3D-optoelectronic SMART system (BTS Bioengi-

neering, Milano, Italy). This system consists of six video

cameras detecting infrared reflecting markers (spheres of

5-mm diameter) at a sampling rate of 120 Hz. Spatial reso-

lution of the system is 0.3 mm. The infrared reflective

markers were attached to the nail of the participant’s right

thumb and index finger, and another marker was attached to

the participant’s right wrist. The markers attached to the

thumb and index finger were used to analyse the grasp

kinematics, whereas the marker attached to the wrist was used

to analyse the kinematics of reaching and lifting. The data of

Exp Brain Res (2012) 218:539–549 541

123

the recorded movements were analysed using a software

developed using MATLAB version 7.7 (R2008b). Recorded

data were filtered using a Gaussian low pass smoothing filter

(sigma value, 0.93). The time course of reach-grasp and lift

was visually inspected: the beginning of the grasp was con-

sidered to be the first frame in which the distance between the

two markers placed on the right finger tips increased more

than 0.3 mm (spatial resolution of the recording system) with

respect to the previous frame. The end of the grasp was the

first frame after the beginning of finger closing in which the

distance between the two right fingers decreased less than

0.3 mm with respect to the previous frame. The beginning of

the reach was considered the first frame during which the

displacement of the reach marker along any Cartesian body

axis increased more than 0.3 mm with respect to the previous

frame. To determine the end of the reach we calculated,

Fig. 1 Experimental set-up and stimuli presented in experiments 1–4. Examples of the movements executed by the participants in the four

experiments are shown

542 Exp Brain Res (2012) 218:539–549

123

separately for the X, Y and Z axes, the first frame following

movement onset in which the X, Y and Z displacements of the

reach marker decreased less than 0.3 mm compared to the

previous frame. Then, the frame endpoint temporally closer

to the grasp end frame was chosen as the end of the reach. The

frame immediately successive to the reach end was consid-

ered as the lift beginning, while the lift end corresponded to

the frame in which the highest point of the hand trajectory was

reached during lifting.

The grasp was studied by analysing the time course of the

distance between the index finger and thumb markers. From

a pinch position, the grasp component is constituted by an

initial phase of finger opening up to a maximum (maximal

finger aperture) followed by a phase of finger closing on the

object (Jeannerod 1988). We measured the following grasp

parameters: peak velocity of finger closure and peak

acceleration of finger closure. Concerning the reach, we

measured reach peak velocity and reach peak acceleration.

Concerning the lift, we analysed the maximal curvature of

the lift trajectory along the lateral axis (left-to-right, z-axis)

of the participants. The maximal curvature is defined as the

maximal distance (on the z-axis) of the wrist trajectory from

the straight line connecting the beginning and end of lift.

Data analysis

Repeated measures ANOVAs were carried out on the mean

values of the grasping-reaching-lifting parameters. The

within-subjects factor was distractor (no distractor vs

sphere vs apple). In all analyses, post hoc comparisons

were performed using the Newman–Keuls procedure. The

significance level was fixed at p = 0.05. When a factor was

significant, we also calculated the effect size [gp2 (partial)].

Results and discussion

The closing phase of the grasp was affected by the presence

of the distractors. Indeed, peak acceleration of finger clo-

sure was significantly lower when the two distractors were

presented [(F(2,14) = 3.99, p = 0.042, gp2 = 0.4]. Post

hoc analysis showed a significant difference between the

no-distractor condition and the conditions of presentation

of the sphere and apple (p = 0.035 and p = 0.05 respec-

tively, Fig. 2). Post hoc analysis also showed no significant

difference between apple and sphere (p = 0.84). Arm peak

acceleration was affected by factor distractor, decreasing

when either the sphere or the apple was presented

[F(2,14) = 5.12, p = 0.021, gp2 = 0.4, post hoc test,

p = 0.017 and p = 0.033 respectively, Fig. 2]. Post hoc

analysis also showed that there was no significant differ-

ence between the apple and the sphere (p = 0.9). Z max-

imal curvature during lifting was affected by the presence

of the distractors [F(2,14) = 4.24, p = 0.036, gp2 = 0.4,

Fig. 2]. Post hoc analysis showed that when either the

apple or the sphere was presented, subjects’ trajectory

deviated to the right, that is in the opposite direction with

respect to the distractor position (p = 0.047 and p = 0.03

respectively). No significant difference was found between

the two distractors (post hoc test, p = 0.78). Other results

are reported in Table 1.

The results of the present experiment suggest that the

sequence of reaching-grasping and lifting was interfered by

the presence of both the apple and the sphere since the grasp

and reach slowed down and the lift trajectory veered away

from the distractor. However, this interference seemed to be

independent from the semantic category of the distractor.

This can be explained by the fact that even if the sphere was a

manipulable artefact as the bottle was, it was not an artefact

with any specific function of interaction with the bottle. The

sphere was placed in a background (the table) so that the

thematic spatial relationships with the bottle were weaker

than the apple because they were less frequent. Nevertheless,

concerning the thematic spatial relationships with the bottle,

no different interference effect was found between apple and

sphere. Consequently, the interference could be based on

motor programmes which, for both the sphere and the apple,

took into account extrinsic and intrinsic object properties

(structural affordances).

Experiment 2

In experiment 2, we addressed the problem of whether an

artefact distractor, that is a glass, potentially compatible,

from a functional point of view, with the artefact target,

that is a bottle, induced interference. Moreover, we tested

whether the actuality of the functional compatibility of the

distractor played a role in inducing interference. We pre-

sented as distractors the following objects: a glass filled

with orange juice (compatible artefact object) and an apple

(the natural object presented in experiment 1). As a matter

of fact, the glass was semantically and functionally com-

patible with the bottle, but, being filled, actually it was not.

Methods

Participants

A new sample of eight right-handed (Oldfield 1971), naıve

volunteers (4 women and 4 men, age 20–29 years) took

part in the experiment.

Apparatus, stimuli and procedure

Apparatus and procedure were the same as in experiment 1.

The distractors were the yellow apple presented in

Exp Brain Res (2012) 218:539–549 543

123

experiment 1 and a glass (*7 cm width,*8 cm eight) filled

with orange juice (Fig. 1). The no-distractor condition was

not included in the procedure; consequently, the experi-

mental session consisted of a single block of 30 trials.

Data recording and analysis

Data recording and analysis were the same as in experi-

ment 1. Repeated measures ANOVAs were carried out on

mean values of the grasping-reaching-lifting parameters,

considering as within-subjects factor distractor (apple vs

filled glass). The significance level was fixed at p = 0.05.

Results and discussion

No differences were found between the kinematics of the

sequence directed to the bottle when the apple and the filled

glass were presented (Table 1). The glass, although of the

same category and functionally compatible with the bottle,

could not induce an interference different from that of the

Fig. 2 Kinematic parameters of

grasp, reach and lift collected in

experiments 1–4, which resulted

significant in the ANOVAs.

Bars are SE. In the panel

showing Z maximal curvature,

positive and negative values

refer to movements directed to

the left and to the right,respectively

544 Exp Brain Res (2012) 218:539–549

123

apple. This can be explained by the fact that the glass was

filled with juice and consequently, actually, it could be not

filled anymore. In other words, it was potentially compatible

with the bottle from a functional point of view, but actually it

was not. Note that the thematic spatial relationships of the

bottle with the glass are stronger than those with the apple,

because a bottle is more frequently presented with a glass

than with an apple. Nevertheless, no different interference

effect was found between glass and apple.

Experiment 3

We compared the effects of a distractor that actually was

functionally compatible with the bottle (an empty glass)

with those of the same distractor actually not compatible (a

glass filled with orange juice).

Methods

Participants

A new sample of eight right-handed (Oldfield 1971), naıve

volunteers (5 women and 3 men, age 23–28 years.) took

part in the experiment.

Apparatus, stimuli and procedure

Apparatus and procedure were the same as in experiment 2.

The distractors were the glass either filled with orange juice

or empty (Fig. 1).

Data recording and analysis

Data recording and analysis were the same as in experiment 2.

In the repeated measures ANOVAs, the levels of the within-

subjects factor distractor were filled glass versus empty glass.

Results and discussion

Peak velocity of finger closure was affected by distractor. The

participants closed their fingers faster when the empty glass

was presented as compared to the filled glass [F(1,7) = 16.13,

p = 0.005; gp2 = 0.7, Fig. 2]. Arm peak velocity was lower

when the empty glass was presented [F(1,7) = 14.58, p =

0.007; gp2 = 0.7, Fig. 2]. Other results are reported in Table 1.

The effects of the presentation of an empty glass on grasp

and reach as compared to a filled glass could be consequent to

the effects of an automatically activated programme of pour-

ing. In order to test whether this could be the case, we com-

pared the kinematics of a sequence of pouring orange juice

contained in a bottle into a glass with those of lifting the bottle.

Experiment 4

Methods

Participants

A new sample of eight right-handed (Oldfield 1971), naıve

volunteers (4 women and 4 men, age 22–29 years.) took

part in the experiment.

Table 1 Results of ANOVAs performed on kinematic parameters

Grasp Reach Lift

Peak velocity of

finger closure

Peak acceleration of

finger closure

Arm peak

velocity

Arm peak

acceleration

Z maximal

curvature

Experiment 1

Distractor levels: null versus

apple versus sphere

F(2,14) = 2.2

p = .146

n.s.

F(2,14) = 3.99

p = .042

gp2 = 0.4

Figure 2

F(2,14) = 1.06

p = .371

n.s.

F(2,14) = 5.12

p = .021

gp2 = 0.4

Figure 2

F(2,14) = 4.24

p = .036

gp2 = 0.4

Figure 2

Experiment 2

Distractor levels: apple

versus filled glass

F(1,7) = 1.23

p = .304

n.s

F(1,7) = 0.11

p = .746

n.s

F(1,7) = 0.98

p = .358

n.s

F(1,7) = 0.77

p = .409

n.s

F(1,7) = 1.08

p = .332

n.s

Experiment 3

Distractor levels: filled

versus empty glass

F(1,7) = 16.13

p = .005

gp2 = 0.7

Figure 2

F(1,7) = 2.44

p = .162

n.s.

F(1,7) = 14.58

p = .007

gp2 = 0.7

Figure 2

F(1,7) = 3.74

p = .094

n.s.

F(1,7) = 1.51

p = .258

n.s.

Experiment 4

Object levels: overturned versus

filled versus empty glass

F(2,14) = 4.05

p = .041

gp2 = 0.4

Figure 2

F(2,14) = 4.66

p = .028

gp2 = 0.4

Figure 2

F(2,14) = 1.08

p = .365

n.s.

F(2,14) = 1.7

p = .218

n.s.

F(2,14) = 126.1

p \ .0001

gp2 = 0.9

Figure 2

The factor was distractor or object

Exp Brain Res (2012) 218:539–549 545

123

Apparatus, stimuli and procedure

Apparatus and procedure were the same as in experiment 2.

The participants were required to reach-grasp and lift the

bottle when a glass filled with orange juice or an over-

turned glass was presented. When an empty glass was

presented, they were required to reach-grasp and pour the

orange juice contained in the bottle into the glass (Fig. 1).

Data recording and analysis

Data recording and analysis were the same as in experi-

ment 2. The lift end corresponded to the frame in which the

highest point of the pour and lift trajectory was reached. In

the ANOVAs, the levels of the within-subjects factor

object were empty glass (to pour) versus filled glass (to lift)

versus overturned glass (to lift).

Results and discussion

Peak velocity [F(2,14) = 4.05, p = 0.041, gp2 = 0.4, Fig. 2]

and peak acceleration [F(2,14) = 4.66, p = 0.028,

gp2 = 0.4, Fig. 2] of finger closure decreased when grasping

with the intention of pouring. Post hoc analysis showed that

the two parameters were significantly lower when pouring

than lifting (peak velocity: filled glass, p = 0.039, over-

turned glass p = 0.05; peak acceleration p = 0.034 and

p = 0.03). The two conditions of lifting did not differ from

each other (peak velocity p = 0.74; peak acceleration

p = 0.67). As expected, the Z maximal curvature was

greater in the pouring than in the lifting [F(2,14) = 126.1,

p \ 0.0001, gp2 = 0.4, post hoc test p = 0.0002 for the both

conditions of lifting, Fig. 2]. No statistical difference was

found between the two conditions of lifting (p = 0.93).

The finding that peak velocity of finger closure was

lower during grasping for pouring indicates that the grasp

was more accurately executed in order to allow a more

stable holding during a successive pouring. In addition, this

datum leads us to speculate that inhibition of the pouring

programme in experiment 3 could have produced an

increase in this parameter. This effect could be considered

as equivalent to trajectory deviation away from distractor

found in the present and previous studies (e.g. Tipper et al.

1991, 1997). Moreover, inhibition during reach in order to

pour interfered with movement execution by slowing down

it.

General discussion

The present study aimed at determining whether, in a task

of reaching-grasping and lifting an artefact, the presenta-

tion of another artefact, functionally compatible with the

target, automatically activated a programme of interaction

between the two objects, which modified the kinematics of

an actual different sequence.

In experiment 1, we compared the effects of two dis-

tractors belonging to different semantic categories (arte-

fact, i.e. a sphere and natural object, i.e. an apple) on the

kinematics of reaching-grasping and lifting the bottle (an

artefact target). The reach and grasp components slowed

down in comparison with the condition of no-distractor

presentation, and, in addition, the trajectory of hand lifting

veered away from distractor position. These results are in

agreement with previous studies (e.g. Tipper et al. 1991,

1997), which hypothesized an encoding of distracting

stimuli in terms of action-based representations. These

representations were inhibited during selection of the target

and interfered with ongoing movement.

No difference in interference effect was observed

between natural and artefact distractors. This result seems

to be at odds with those by Kritikos et al. (2001). These

authors manipulated size and semantic category of the

distractors and found an effect of both of these character-

istics on grasp. However, two main differences should be

observed between the stimuli presented in the present study

and those by Kritikos et al. (2001). First, in the present

study, the distractors were approximately of the same size,

whereas distractors of different size were presented in

Kritikos et al.’s study (2001). Second, in the present study

the distractors were never used as targets, whereas this

occurred in Kritikos et al.’s study (2001). Thus, the fact

that interfering programmes varied according to distractor

size and the same distractors were also actually grasped

could increase the probability to make evident an effect of

the category which could be under-threshold for distractors

of fixed sizes. Finally, it is important to stress that the main

purpose of the present study was not to compare the effects

between distractors of different semantic categories, but the

effects of artefact distractors, which, when functionally

compatible with an artefact target, could activate pro-

grammes of interaction affecting the actual action directed

to the target.

The results of experiments 2 and 3 showed that, actually,

target and distractor should be functionally compatible in

order to affect the action directed to the target. Indeed, a

programme of pouring could be activated when a bottle

was presented with a functionally compatible distractor,

that is an empty, rather than a filled glass. Concerning the

grasp, in experiment 3, the finger closure on the empty

glass was quicker. We can speculate that this was due to

the fact that a programme of pouring was inhibited. Indeed,

in experiment 4, finger closure was slower when the

reaching-grasping was finalized to pour. Inhibition of

pouring in experiment 3 might have produced an inverse

effect of faster grasping.

546 Exp Brain Res (2012) 218:539–549

123

Tools are tightly coupled to different sequences of

actions characterizing their use; for example, a bottle filled

with liquid can be associated with an action of pouring,

drinking from the bottle, or placing into an ice bucket. In

other words, sequences of arm and hand actions can

develop and become strongly associated with tools fol-

lowing experience of their use. This well-defined set of

action operations is tied to prior experience and is stored as

knowledge of object functions (Valyear et al. 2007). We

propose to use the term working affordance to define the

programme representing a specific sequence of actions

during which an artefact and a functionally compatible

object interact with each other. The term working affor-

dance would indicate a programme of interaction among

artefacts depending not only on intrinsic and extrinsic

properties of objects, but also on stored information about

learned hand–object relations. These representations are

complementary to those mediating visuomotor transfor-

mations (structural affordances) underlying grasping

actions. For these reasons, when two artefacts are present

in a scene, the resulting action is strictly linked to the

functional compatibility (e.g. a bottle and a glass, or a nut

and a nutcracker), to the suitability (i.e. to be in the right

place at the right time) and, in particular, to the actual state

of the artefact (i.e. empty or full; with or without the nut-

shell). A neuroimaging and EEG study (Mizelle and

Wheaton 2010) has shown that the contextual correctness/

incorrectness of tool–object interaction activated distinct

brain regions. Specifically, incorrectness activated tempo-

ral area, cingulate area and insula, whereas correctness

activated parietal and frontal areas. Activation for incor-

rectness preceded correctness. These data are in accordance

with the concepts of compatibility, suitability and actual

state of artefacts proposed for working affordances. Indeed,

Mizelle and Wheaton (2010) suggested that activation of

insula and superior temporal cortex may serve as a

‘‘gatekeeper’’, for the evaluation of the contextual cor-

rectness of possible interactions between presented arte-

facts (e.g. bottle with empty glass). Once the correctness

was verified, the fronto-parietal areas were activated in

order to derive the adequate sensorimotor representation

and motor plan for that artefact–action goal pair. In the

case of incorrectness, the insula/superior temporal areas

might serve to generate signals allowing for appropriate

perception of tool use error. Thus, we can expect a fronto-

parietal activation when a bottle was presented with an

empty glass, and a insula/superior temporal area activation

when the bottle was presented with a full glass.

The function of the bottle or the glass might be con-

sidered that of liquid container only. Nevertheless, the

simple function to contain a liquid is not the only reason

why these artefacts are made. The reason for making them

is the intention of using them for pouring or drinking. In

this sense, a working affordance would reflect the possi-

bility to prepare a sequence of actions according to a final

intention (e.g. lifting the bottle with the intention of filling

the empty glass) and on the basis of motor experience (e.g.

simulating a sequence based on motor experience rather

than visual salience, Pezzulo et al. 2010). The working

affordance not only influences object detection (functional

affordance) as found by Riddoch et al. (2003) but it

implicitly changes parameters of the sequence even in the

absence of any explicit task to use the objects (target and

distractor) together. Following this hypothesis, a working

affordance would be activated whenever a target-artefact is

presented even with natural objects as long as the two

objects are functionally compatible. For example, grasping

a knife in the presence of an apple may more easily activate

a programme of peeling. This raises the possibility that

objects of whatever category (artefact or natural object)

presented with an artefact target may contribute to evoke

working affordances.

Neurophysiological studies have described a number of

areas within the frontal and the posterior parietal cortex

that is involved in the control of actions executed with tools

(Culham and Valyear 2006; Valyear et al. 2007). These

tool-related imaging studies reported activation of anterior

portion of the intraparietal sulcus (IPS), inferior parietal

lobule, ventral premotor cortex (VPM) (Binkofski et al.

1999; Chao and Martin 2000; Johnson-Frey 2004; Kel-

lenbach et al. 2003; Gerlach et al. 2002; Grabowski et al.

1998), medial fusiform gyrus (Beauchamp et al. 2002,

2003; Chao et al. 2002; Devlin et al. 2005; Whatmough

et al. 2002). Therefore, it is possible to suppose that tools

can activate a parietal-frontal circuit including parietal

lobe, IPS and VPM; this circuit seems to be involved on

motor planning and on motor execution. Ideomotor apraxia

(IM) is often associated with parietal lesions, specifically

regions encompassing parts of the IPS (Buxbaum et al.

2005; Haaland et al. 2000). IM patients poorly perform on

tasks associated with planning artefact-related movements;

they are characterized by the inability, once they recalled

the mental representation of movement required, to acti-

vate the correct motor sequence to implement the move-

ment itself: the patient knows ‘‘what’’ to do, but he does

not know ‘‘how’’ to do it. Thus, we can expect a deficient

retrieval of specific interactions between functionally

compatible artefacts (Buxbaum et al. 2003).

Conversely, neuropsychological studies conducted on

patients with damage to the frontal lobes showed ‘‘utili-

zation behaviour’’ (Lhermitte 1983): in these patients, an

object elicits a stereotyped action, inappropriate in the

context. For example, if there is a glass within the reach of

the patient, he will grasp it; if a bottle of water is also

placed on the desk, he will grasp this too and then will pour

water into the glass and will drink it. The same occurs also

Exp Brain Res (2012) 218:539–549 547

123

when the patients have been instructed to carry out other

tasks (Shallice et al. 1989). A possible explanation for this

behaviour is that the inhibitory function of the frontal lobes

on the parietal lobes is suppressed; the result is a lack of

inhibition mechanism on the parietal lobes, including the

areas specialized for the control of actions executed with

tools. In other words, patients with damage to the frontal

lobes are unable to control the working affordances

induced by two or more functionally compatible artefacts.

Consequently, we expect a lack of working affordances in

apraxic patients, and, conversely, an insufficient control of

them in patients with prefrontal lesions.

Summing up, these data support the idea that when two

artefacts are presented in a scene, they do not only auto-

matically and obligatorily activate the affordance that they

usually can afford when presented alone. In fact, our results

provide evidence for the notion that the processing of

artefact features depends on the contextual information. As

contextual information, we refer to objects that are func-

tionally compatible with the target and activate specific

(working) affordances related to the potential interaction of

the target with the objects presented in the scene.

Acknowledgments We thank Claudio Secchi for help in carrying

out the experiments and analysing the data. The work was supported

by grant from MIUR (Ministero dell’Istruzione, dell’Universita e

della Ricerca) to M.G.

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