In cognitive science and experimental psychology, most of the empirical research has studied affordances in relation to the design of common objects, focusing mostly on their shape and size (e.g., Ellis & Tucker, 2000). Nowadays, it is widely accepted that our readiness for action, evoked by certain properties of the objects, is modulated by several aspects that convey the interaction between subject, object, and context. As described before, graspability, distance, presence of others, ownership, social norms, and language are just about some of these elements, all of which are closely related to the perception of perceptually guided actions (Varela et al., 1991).
Here, we explored the modulation of affordances in relation to the material from which objects are made. Materials are not only a fundamental component of the object’s aesthetic expression and functionality (Barati & Karana, 2019), they also can play a crucial role in the appreciation and evaluation of it (Harper, 2018). Particularly, this aspect pushed us to interweave affordance research methodology with some theoretical premises related to the perception of an aesthetic experience. The present study is based on the idea that, when comparing similar objects made of different materials, the aesthetic-evaluative component may play an important role in stimulating (or inhibiting) the activation of affordances. Our tastes, preferences, and knowledge-experience components play a crucial influence on perception (and thus on our actions), which has been shown in art and aesthetic objects (Pelowski et al., 2016). The type of material that an aesthetic object consists of may trigger the effect of these components, perhaps even more so than other properties. Indeed, the change of material is a choice that entails various implications. First, the material is an element characterized by different components, such as texture, color, or brightness, and it is not easy to discriminate how all these features interact with our perception (Treisman, 1998). Visual perception is not always able to estimate physical parameters of materials and objects (Fleming, 2014), but at the same time we visually recognize textures easily in everyday life regardless of the shape of the objects (Julesz, 1965). Here, we investigated the affordances by measuring response times to visual stimuli manipulating material’s sustainability. Thus, we initially examined different options for sustainable and non-sustainable materials applicable to everyday objects of common use and, finally, we opted for wood and plastic. The ratings we collected after the experimental session showed some expected significant differences (i.e., wooden objects were rated as more pleasurable, sustainable, and less familiar than plastic ones), thus confirming the validity of our experimental choice in terms of materials.
To measure affordances, we adopted the paradigm employed by Costantini et al. (2011) and Ambrosini et al. (2012), to which we added a new independent variable, the surface material. In one study, the authors investigated the difference between the actual and the estimated reaching space for everyday objects’ affordances in relation to the simulation formed during language comprehension (Ambrosini et al., 2012). Participants were faster at responding to manipulation and function verbs primed by the actual rather than the estimated reaching position of the object. Those results showed that the difference between the reachable and non-reachable space is entailed by the possibility of interacting with objects physically and realistically; i.e., an object suggests an action only when it falls within the actual reaching space of the perceiver - when an actual interaction is possible.
In the present study, we changed the way to respond (button press instead of finger release and mimicking of the gesture), and we used only two object distances (namely, near and far), as our main focus here was not on graspability in relation to space. We also replaced the pointing verbs with a new category, the interaction verbs (i.e., verbs that entail actions in which another person is involved). This choice was based on our interest in investigating the social dimension of certain actions and how they may change in relation to the object’s material and the object’s distance from the perceiver. Finally, we also introduced the Pro-Environmental Behavior Scale (PEBS) to see if any change in the affordances’ activation could eventually be related to the participants’ environmental sensitivity. The Theory of Planned Behavior (TPB) conceives behavior as induced by attitudes and subjective norms (Ajzen, 1991). Indeed, the alignment of these factors also seems to occur for pro-environmental behavior (Gifford et al., 2011). Moreover, individual environmental values and beliefs also play a crucial role (Stern, 2000). Since this scale is representative of several personal traits, and object properties are contained in stored knowledge built up from the past (Osiurak et al., 2017), we assumed that this measure may influence the affordances activation in relation to sustainable and non-sustainable materials. However, we expected the plastic objects to be still advantaged because of their prototypicality, regardless of the PEBS results.
Our analysis found a surprising difference between the two blocks of trials. As shown in the results session, there was a significant effect of the Block factor, with faster RTs for the second one, and also a significant effect of the sub-block factor within Block 1, with faster RTs for the last sub-block, which led us to assume a learning effect in the first part. The following discussion will regard only the significant results, which were present only in the second block.
In general, we observed a main effect of materials with RTs faster for wooden objects compared to plastic ones. This result was surprising since we were expecting plastic objects to be advantaged for their familiarity. Familiarity is a background understanding that actors need to deal with the world and equipment in an absorbed and non-deliberate way (Riemer & Johnston, 2017), embedded in know-how (Riemer & Johnston, 2014), related to specific contexts and accumulated through practice or experience (Turner, 2005). Furthermore, plastic objects are not only more familiar but also more frequently used in Italy (e.g., Campanale et al., 2019; Foschi et al., 2021), and both features (object familiarity and frequency of use) can be determinants for the activation of affordances (Rio, 2019). Nevertheless, this result shows that wooden objects had an advantage despite their unfamiliarity and less frequent use. For some theories of visual perception (Varadarajan, 2011), the material should be considered as one of the key features for affordances (along with, e.g., shape and color), on which object recognition is grounded and through which humans are capable of categorizing previously unseen objects with uncharacteristic texture into its right class, without a priori knowledge (Varadajan & Vincze, 2012, p. 515). If this argument upholds, the advantage found for wood might not be related to the familiarity or frequency of the use of the respective objects, but instead to some other intrinsic characteristics of the material.
Moreover, we also found the main effect of verbs; function verbs were the verbs category associated with faster RTs compared to manipulation, observation, and interaction. The advantage of function verbs over manipulation and observation verbs indicates that objects are represented in terms of their use. This is in line with previous evidence with the same paradigm that involved linguistic stimuli (Ambrosini et al., 2012; Costantini et al., 2011). Other studies have found that structural-volumetric responses are activated faster than functional actions (e.g., Jax & Buxbaum, 2010). However, contrary to our work, these studies focused on conflict objects; i.e., objects that evoke two different grasping actions for manipulation and function; in addition, they did not employ linguistic stimuli combined with object images.
Most importantly, we observed a significant interaction between materials, verbs, and object locations. Results showed significantly greater facilitation for plastic compared to wooden objects when presented in the near space and followed by function verbs. Function verbs seem to have a strong connection with plastic objects, which may be consistent with the fact that plastics are tightly related to their functionality (Evode et al., 2021). Language has a privileged relationship with function (see, for instance, Kemler Nelson et al., 2000; Masson et al., 2008), and the use of plastic in the last decades has increased as never in history (Freinkel, 2011). Hence, the simulation conveyed by function verbs in the near space may have been stronger with plastic, likely because it is the more commonly used and familiar. Thus, even if all objects were perfectly recognizable, regardless of the material, the plastic ones had reason to be advantaged within the function-near frame.
Conversely, with interaction verbs, a general advantage for wooden objects was found. Interestingly, with these verbs, the effect seems more pronounced when the object was placed at a far distance (non-reachable) since responses in the wood-far condition were significantly faster compared not only to the plastic-far, but also to the plastic-near and wood-near condition. At the same time, responses in the wood-near condition were shorter than the plastic-far ones, and the plastic-near condition was still significantly faster than the plastic-far, so an advantage due only to the distance variable (i.e., the far-reaching condition) needs to be excluded. Instead, a specific interplay between two variables is present within the interaction-verbs category, where wooden objects placed in a far-reaching space have a predominant advantage. Notably, interaction verbs have never been used with this kind of paradigm, therefore they are not forcibly related to the object’s distance from the perceiver in the same way as the other types of verbs. Indeed, interaction verbs seem not related with the near distance as it is for functionality, and the advantage of the far distance could be due to the hypothetical presence of another person with whom the interaction would take place (Scorolli et al., 2016). Moreover, the durability, the re-usability, and thus the perceived higher value of wooden objects (Ilker, 2016) might lead people to represent them as more precious than the plastic ones, which are commonly regarded as more disposable (Oberoi & Garg, 2021; Oberoi et al., 2021). Notably, almost half of the total production of plastic is manufactured for single use (Hopewell et al., 2009). Conversely, examples of repair and reuse of wooden things are rooted in human history. For both past and present societies, the fact that wood comes from natural and meaningful living things, such as trees, may have mediated the value afforded to this material and its processing (Sands, 2022), opposed to what may happen with man-made objects (Ismail et al., 2019). Thus, within the interaction context, the relation between the object and its location might have been specifically affected by the material component, in terms that certain inherent properties related to wood could have overcome the distance constraints. Summarizing, the results illustrated so far show that participants are sensitive to the relationship between near and far space, kind of action, and object material. When verbs induce them to simulate objects’ function, participants process plastic objects faster in the near space, likely due to the higher familiarity and usability of plastic. Conversely, they respond to wooden objects faster when they read verbs related to interacting with others, particularly in the far space.
Furthermore, our rating data showed that wooden objects are significantly different from plastic ones in terms of hardness, heaviness, sustainability, and pleasantness.
In terms of hardness and heaviness, the advantage for the lighter plastic objects within the function frame can be considered consistent (Anelli et al., 2010), though we could expect less advantage for the wooden objects also within the interaction frame. The absence of any reaching or grasping task might have attenuated the influence of these two features, as it is the case for the object location within this particular frame.
As for sustainability, one further goal of this study was to verify eventual correlations between the material’s sustainability ratings and the participants’ environmental behavior. Predictive coding theories (Clark, 2013) and the affordance competition hypothesis (Cisek, 2007) suggest that our prior knowledge influences our perception from an earlier stage of processing, so that we then act upon what is more salient for us. Similarly, Cupchik (2020) suggests that aesthetic appreciation takes place from a mere glance. Here, we expected the wooden objects to have at least a shorter gap in response times (compared to the plastic ones) for participants with high scores in the PEB questionnaires, but no correlation of that source was found. One possible explanation can be related to the fact that most of the scores were close to the average (M = 3.14; SD = 0.467): only two participants had a mean score above 4 (maximum score was 5). Thus, we did not find a modulation between the pro-environmental behaviors and RTs. Moreover, although we employed young participants and used the well-adapted version of the questionnaire to the Italian context made by Menardo and colleagues (2019), scores were not as high as we expected. For only two out of four PEB sub-scales (namely, Conservation and Transportation) we found high scores, probably because in the context where the participants were recruited (Bologna, Italy) bikes and public transportations are frequently used and well implemented (Bertini et al., 2023; Sperati & Colazzo, 2018). Conversely, we found low mean scores for the Environmental Citizenship and Food sub-scales.
Notably, aesthetic evaluations often overlap, so that ratings of pleasantness could be analogous to ratings of beauty or liking (Augustin et al., 2012; Jacobsen, 2006). Thus, in the context of this study, when participants are evaluating wooden objects as more pleasant than plastic ones, what is actually being captured is the aesthetic assessment of beauty. With the term beauty, here we are referring to a pleasurable subjective experience directed toward an object, which makes the concept of beauty interchangeable with that of aesthetic pleasure (Reber et al., 2004, p. 365). Even if pleasure and beauty are not strictly comparable, they can be considered equivalent in terms of their affective component when people appraise objects (Skov & Nadal, 2021). Indeed, considering that an object causes aesthetic pleasure for those who contemplate it as beautiful (Ducasse, 1944), the aesthetic pleasantness can be associated with the personal judgment of beauty (McGreal, 1949). Beauty may depend on identification with an object (i.e., the human need to express oneself through objects) and the product's ability to communicate important personal values (Hassenzhal, 2004). Therefore, since the rating question was “Do you like this object?”, entailing a personal evaluation, we here imply beauty as the aesthetic pleasantness appraisal related to the participants’ personal tastes. Although our control analyses with the ratings showed that the level of rated pleasantness can not explain the faster RTs for the wooden objects, there is reason to hypothesize that in our case their aesthetic pleasure might have had a greater influence than the other features. Notably, beauty is less dependent on a grasping task (unlike hardness or heaviness) or a more reflective evaluation (as it is for sustainability). Studies about beauty have demonstrated that liking can be connected to an initial aesthetic-perceptive network, which starts very early (Cela-Conde et al., 2013), and that our affective processes in relation to an aesthetic experience also start at the early stages, influencing the salience and attention toward the beautiful object (Leder et al., 2004, 2014). Moreover, pleasant emotions derived from beauty may also be related to surprise and novelty induced by something perceived as not ordinary (Pelowski et al., 2017). Indeed, the appraisal of novelty and the disruption of processing expectations are linked to the kind of pleasure derived from beauty (Armstrong & Detweiler-Bedell, 2008). Perhaps, the pleasure of sustainable objects lies also in their ability to disrupt the user’s comfort zone, and the use of unexpected materials confront our powers of perception and conception (Harper, 2018). In this light, we can assume that beauty might have transversely influenced the activation of affordances, and we can speculate how this occurred within the different frameworks.
For instance, despite the main effect for wood material (i.e., shorter RTs for wood than for plastic objects), plastic is still faster when is in the near-space and encoded in relation to individual action verbs (e.g., function), while wooden objects may be considered as more precious so to induce slower reactions. Indeed, the nature of beauty is rather self-oriented than goal-oriented (Hassenzhal, 2004).
Strikingly, with observation verbs, we found a significant advantage for plastic in the far-reaching space (RTs for plastic-far are lower than those associated with wood-far and even with plastic-near). In contrast, we found significantly faster responses for wooden objects when placed in the near-space. Notably, observation is easier and more effective when objects are close (Shelton et al., 1990). In this case, when placed closer, the wooden objects are more salient than the plastic ones. At the same time, objects placed in a far-reaching position may lose salience (Hoffman & Singh, 1997, leading to a more automatic way of perception to instead be activated, thus the more familiar objects were processed the fastest. In other words, wooden objects might have been perceived more for their beauty (with beauty referring to the aesthetic pleasantness of the object in this case) rather than for the action that is associated with them. This would mean that an aesthetic mode of perception is activated in which the beautiful object is contemplated. This kind of interpretation could be linked to the phenomenological dimension of an aesthetic experience (Shustermann, 1997), for which we may have a shift in attention from goal-directed to aesthetic-directed, and it would connect this phenomenon to the ongoing debate about the lack or reduction of action purposes within the aesthetic experience (Mastandrea, 2020). In this sense, we hypothesize that the affordances activated by the wooden objects (which are rare and less used) may be of a sort of different nature from those activated by the plastic and more commonly used objects, the former being more of an aesthetical kind (aesthetic affordances).
Finally, results with interaction verbs open new questions about how the hypothetical presence of another person might influence affordances, producing different effects. It may accelerate certain responses (since the command and final goal is to give it to someone), or it can create an expectation from the other (one of the interaction verbs was “receive”); finally, the aesthetic attractiveness of the object can interfere with a sense of ownership or its donation as a gift (e.g. with the verb “offer”). In our case, wooden objects (considered significantly more beautiful), when primed by certain interaction verbs and placed in the far-reaching space, could be perceived as owned by someone else, thus activating aesthetic networks more linked to the desire of the object; i.e., brain regions related to wanting rather than liking (Berridge et al., 2009). According to Berridge and colleagues, liking represents pleasure unrelated to the desire for possession, whereas wanting is related to the desire for the object and connected with the actions necessary to satisfy that desire, and the two mechanisms seem mediated by different neural circuits and neurochemical systems (Yue et al., 2007; Nadal, 2013; Tibboel et al., 2015). Some authors have argued that this difference may somehow support with neural evidence the specificity of an aesthetic emotion (e.g., Chatterjee, 2014). Here, we are only assuming that the affordances activated by certain kinds of objects, which have the shape and dimension of everyday objects but are considered rarer and more beautiful than their common alternative, may have been significantly influenced by an aesthetic component induced by the material. However, further research is needed to better investigate this relation between affordances, aesthetics and object material. .