Grasping spheres, not planets

The visual size is enough to automatically induce the potentiation of grasping behaviours

Seeing objects usually grasped with a power or a precision grip (e.g., an apple vs a cherry) potentiates power- and precision-grip responses, respectively. An embodied account suggests that this effect occurs because object conceptual representations would lie on a motor simulation process. A new account, named the size-coding account, argues that this effect could be rather due to an overlapping of size codes used to represent both manipulable objects and response options. In this article, we investigate whether this potentiation effect could be merely due to a low-level visual feature that favours a size-coding of stimuli: the visual size in which objects are presented. Accordingly, we conducted two experiments in which we presented highly elementary and non-graspable stimuli (i.e., ink spots) either large or small rather than graspable objects. Our results showed that the mere visual size automatically potentiates power- and precision-grip responses that are in line with the size-coding account of the potentiation effect of grasping behaviours. Moreover, these results appeal to improve the methodological control of the size of stimuli especially when researchers try to support the embodied account.

The visual size of graspable objects is needed to induce the potentiation of grasping behaviors even with verbal stimuli

Merely perceiving objects usually grasped with a power or a precision grip (e.g., an apple vs. a cherry) potentiate power-grip and precision-grip responses, respectively. According to the size-coding account, this potentiation effect is due to the compatibility between size codes associated with both stimuli and responses, rather than to the simulation of motor information stored at a conceptual level (i.e., the embodied account). At the stimulus level, size-coding would occur, because objects associated with a power grip are usually presented in a larger visual size than objects associated with a precision grip. However, this explanation is challenged by results, showing that reading nouns of objects associated with power or precision grip also leads to potentiation effects, even though the visual size of the displayed object is no longer perceived. Therefore, we designed three experiments to better understand this word-based potentiation effect and to investigate whether it relies on size codes. Our results showed a word-based potentiation effect only when the object nouns were interleaved with pictures depicting the objects in their typical visual size. We discuss the contributions of these results for both the size-coding account and the embodied account of the potentiation effect of grasping behaviors.

Influence of colour on object motor representation

Colour conveys specific information about the status/quality of an object; whereas its role in object recognition has been widely studied, little is known about its role in sensorimotor processes. We performed three experiments to assess whether colour influences the motor representation of graspable objects. In Experiment 1, we used a grasp compatibility task, in which participants categorized each object as natural or artifact, by performing reach-to-grasp movements. Response grasps could be compatible or incompatible with the ones normally used to manipulate the objects. Results showed faster reaction times for natural objects displayed in the correct colour compared with both opposite colour and correct colour artifact objects. In Experiment 2, to directly assess the effect of colour on object motor representation, we used an interference task in which an irrelevant object was shown while performing a pre-specified reach-to-grasp movement (i.e., verbal cues: small vs. large). Results highlighted a reversed compatibility effect when objects were shown in their correct colour, but only at the beginning of the movement (10 ms SOA). Finally, we run a third experiment using the same task as in Experiment 2. In this experiment, we compared the grasp compatibility effect driven by natural objects with the grasp compatibility effect driven by dangerous natural objects (e.g., cactus), which are objects that should not elicit a grasping program. The results of Experiment 3 confirm those of Experiment 2, highlighting also specific processes related to dangerous objects. Taken together, these results revealed that colour can be significant for the motor system, highlighting the close link between colour and shape, and also specific processes related to dangerous objects.

Facilitation of allocentric coding by virtue of object-semantics

In the field of spatial coding it is well established that we mentally represent objects for action not only relative to ourselves, egocentrically, but also relative to other objects (landmarks), allocentrically. Several factors facilitate allocentric coding, for example, when objects are task-relevant or constitute stable and reliable spatial configurations. What is unknown, however, is how object-semantics facilitate the formation of these spatial configurations and thus allocentric coding. Here we demonstrate that (i) we can quantify the semantic similarity of objects and that (ii) semantically similar objects can serve as a cluster of landmarks that are allocentrically coded. Participants arranged a set of objects based on their semantic similarity. These arrangements were then entered into a similarity analysis. Based on the results, we created two semantic classes of objects, natural and man-made, that we used in a virtual reality experiment. Participants were asked to perform memory-guided reaching movements toward the initial position of a target object in a scene while either semantically congruent or incongruent landmarks were shifted. We found that the reaching endpoints systematically deviated in the direction of landmark shift. Importantly, this effect was stronger for shifts of semantically congruent landmarks. Our findings suggest that object-semantics facilitate allocentric coding by creating stable spatial configurations.

Effects of grasp compatibility on long-term memory for objects

Previous studies have shown action potentiation during conceptual processing of manipulable objects. In four experiments, we investigated whether these motor actions also play a role in long-term memory. Participants categorized objects that afforded either a power grasp or a precision grasp as natural or artifact by grasping cylinders with either a power grasp or a precision grasp. In all experiments, responses were faster when the affordance of the object was compatible with the type of grasp response. However, subsequent free recall and recognition memory tasks revealed no better memory for object pictures and object names for which the grasp affordance was compatible with the grasp response. The present results therefore do not support the hypothesis that motor actions play a role in long-term memory.

Behavioral Bias for Food Reflected in Hand Movements: A Preliminary Study with Healthy Subjects

Palatable food induces general approach tendencies when compared to nonfood stimuli. For eating disorders, the modification of an attention bias toward food was proposed as a treatment option. Similar approaches have been efficient for other psychiatric conditions and, recently, successfully incorporated approach motivation. The direct impact of attentional biases on spontaneous natural behavior has hardly been investigated so far, although actions may serve as an intervention target, especially seeing the recent advances in the field of embodied cognition. In this study, we addressed the interplay of motor action execution and cognition when interacting with food objects. In a Virtual Reality (VR) setting, healthy participants repeatedly grasped or warded high-calorie food or hand-affordant ball objects using their own dominant hand. This novel experimental paradigm revealed an attention-like bias in hand-based actions: 3D objects of food were collected faster than ball objects, and this difference correlated positively with both individual body mass index and diet-related attitudes. The behavioral bias for food in hand movements complements several recent experimental and neurophysiological findings. Implications for the use of VR in the treatment of eating-related health problems are discussed.

Effects of motor congruence on visual working memory

Grounded-cognition theories suggest that memory shares processing resources with perception and action. The motor system could be used to help memorize visual objects. In two experiments, we tested the hypothesis that people use motor affordances to maintain object representations in working memory. Participants performed a working memory task on photographs of manipulable and nonmanipulable objects. The manipulable objects were objects that required either a precision grip (i.e., small items) or a power grip (i.e., large items) to use. A concurrent motor task that could be congruent or incongruent with the manipulable objects caused no difference in working memory performance relative to nonmanipulable objects. Moreover, the precision- or power-grip motor task did not affect memory performance on small and large items differently. These findings suggest that the motor system plays no part in visual working memory.

Motor expertise modulates movement processing in working memory

A substantial amount of literature has demonstrated individuals' tendency to code verbally a series of movements for subsequent recall. However, the mechanisms underlying movement encoding remain unclear. In this paper, I argue that sensorimotor expertise influences the involvement of motor processes to store movements in working memory. Experts in motor activities and individuals with limited motor expertise were compared in three experimental conditions assessing movement recall: (a) without suppression task, (b) with verbal suppression, and (c) with motor suppression. Athletes outperformed controls in movement recall, but the suppression tasks affected the two groups differently. Verbal suppression affected controls more than athletes, whereas the effect was reversed with motor suppression. Together, these findings suggest that controls and athletes favor different mechanisms to encode movements, either based on verbal or on motor processes, providing further evidence for a tight relationship between sensorimotor and cognitive processes.

A functional role for modality-specific perceptual systems in conceptual representations

Theories of embodied cognition suggest that conceptual processing relies on the same neural resources that are utilized for perception and action. Evidence for these perceptual simulations comes from neuroimaging and behavioural research, such as demonstrations of somatotopic motor cortex activations following the presentation of action-related words, or facilitation of grasp responses following presentation of object names. However, the interpretation of such effects has been called into question by suggestions that neural activation in modality-specific sensorimotor regions may be epiphenomenal, and merely the result of spreading activations from “disembodied”, abstracted, symbolic representations. Here, we present two studies that focus on the perceptual modalities of touch and proprioception. We show that in a timed object-comparison task, concurrent tactile or proprioceptive stimulation to the hands facilitates conceptual processing relative to control stimulation. This facilitation occurs only for small, manipulable objects, where tactile and proprioceptive information form part of the multimodal perceptual experience of interacting with such objects, but facilitation is not observed for large, nonmanipulable objects where such perceptual information is uninformative. Importantly, these facilitation effects are independent of motor and action planning, and indicate that modality-specific perceptual information plays a functionally constitutive role in our mental representations of objects, which supports embodied assumptions that concepts are grounded in the same neural systems that govern perception and action.

Approach motivation as incentive salience: perceptual sources of evidence in relation to positive word primes

Four experiments (total N = 391) examined predictions derived from a biologically based incentive salience theory of approach motivation. In all experiments, judgments indicative of enhanced perceptual salience were exaggerated in the context of positive, relative to neutral or negative, stimuli. In Experiments 1 and 2, positive words were judged to be of a larger size (Experiment 1) and led individuals to judge subsequently presented neutral objects as larger in size (Experiment 2). In Experiment 3, similar effects were observed in a mock subliminal presentation paradigm. In Experiment 4, positive word primes were perceived to have been presented for a longer duration of time, again relative to both neutral and negative word primes. Results are discussed in relation to theories of approach motivation, affective priming, and the motivation-perception interface.

Re-appreciating the why of cognition: 35 years after marr and poggio

Marr and Poggio’s levels of description are one of the most well-known theoretical constructs of twentieth century cognitive science. It entails that behavior can and should be considered at three different levels: computation, algorithm, and implementation. In this contribution focus is on the computational level of description, the level that describes the “why” of cognition. I argue that the computational level should be taken as a starting point in devising experiments in cognitive (neuro)science. Instead, the starting point in empirical practice often is a focus on the stimulus or on some capacity of the cognitive system. The “why” of cognition tends to be ignored when designing research, and is not considered in subsequent inference from experimental results. The overall aim of this manuscript is to show how re-appreciation of the computational level of description as a starting point for experiments can lead to more informative experimentation.