Our object recognition abilities, a direct product of our experience with objects, are fine-tuned to perfection. Left temporal and lateral areas along the dorsal, action related stream, as well as left infero-temporal areas along the ventral, object related stream are engaged in object recognition. Here we show that expertise modulates the activity of dorsal areas in the recognition of man-made objects with clearly specified functions. Expert chess players were faster than chess novices in identifying chess objects and their functional relations. Experts' advantage was domain-specific as there were no differences between groups in a control task featuring geometrical shapes. The pattern of eye movements supported the notion that experts' extensive knowledge about domain objects and their functions enabled superior recognition even when experts were not directly fixating the objects of interest. Functional magnetic resonance imaging (fMRI) related exclusively the areas along the dorsal stream to chess specific object recognition. Besides the commonly involved left temporal and parietal lateral brain areas, we found that only in experts homologous areas on the right hemisphere were also engaged in chess specific object recognition. Based on these results, we discuss whether skilled object recognition does not only involve a more efficient version of the processes found in non-skilled recognition, but also qualitatively different cognitive processes which engage additional brain areas.

Introduction

Our object recognition abilities, a direct product of our experience with objects, are fine-tuned to perfection – we need just a split of a second to recognize an everyday object and its function [1]. A dedicated network of left lateralized areas along the ventral and dorsal visual streams has been associated with this amazing feat [2]–[3]. It is less clear, however, whether and how this network enables particularly skilled recognition as found among experts who have extensive experience with domain-specific objects and their functions. Here we show that skilled recognition of chess objects and their functions does not exclusively involve the left lateral areas usually related to normal object recognition. Instead, skilled recognition of chess objects and their functions additionally engage the homologous right regions.

Everyday objects have typical forms that make them recognizable. The ventral visual stream, thought to be essential in object recognition, carries information from the occipital primary visual areas to the inferior-temporal cortex [4]–[5]. A part of the inferior temporal cortex, fusiform gyrus (FG), is thought to mediate the perception of color and form [6]–[7]. The medial part of the left FG participates in everyday object recognition [8]–[9]. Everyday objects, however, have also characteristic functions. This is particularly the case with man-made manipulable objects such as saw or hammer, whose visual features are directly related to their function. These functions are closely coupled to actions which are inevitably associated with movements. The dorsal visual stream is thought to mediate spatially related action [4]–[5]. For example, the posterior middle temporal gyrus (pMTG) at the left lateral side is activated when people name visually or acoustically presented everyday objects, and particularly when they have to retrieve their function [6], [10]–[11]. An explicit retrieval of actions associated with an object is closely associated with the supramarginal gyrus (SMG) in the left inferior parietal lobe (IPL; [3]). The SMG is activated when people are explicitly instructed to retrieve a function-related action with an object [12]–[13] and its activation is particularly modulated by actual execution of an action [14]–[15].

Both, the ventral and the dorsal pathway are more activated in the left than right hemisphere in recognition of manmade objects. This left lateralization probably enables anatomical projections between the object-related brain regions in the left hemisphere [16]–[19].

Although separate characteristics of objects such as form and function engage separate visual streams, recognition of form and function are nevertheless inextricably connected [9]. This reflects our real life experience with objects that are often impossible to recognize without identifying their particular functions. The intrinsic coupling between objects' external features and their functions, as a reflection of our experience with them, has long been recognised in neuropsychology and cognitive neuroscience [10], [20]–[21]. Indeed, a training study of novel objects and their functions [22] indicates that the left lateral (pMTG, SMG/IPL) and left ventral (medial FG) areas mediate recognition of trained artificial objects and their functions.

Although training studies present an excellent way to investigate the impact of prior experience on recognition of objects and their functions, the amount of training in experimental studies is typically limited to a few hours, or in the best case, a few days of training. Yet, in real life, we are exposed to everyday objects for years. From an experimental point of view, it is difficult to measure our experience with objects, and in most cases, we all are familiar with common everyday objects to a similar extent. Here we used the game of chess to circumvent these problems. We employed the expertise approach [23]–[24] to investigate learning related differences in recognition of objects and their functions by comparing expert and novice chess players.

Although chess is a complex cognitive activity that needs years to master [25]–[30], it rests on the recognition of chess specific objects, called pieces, and their functions [31]–[32]. Chess objects are manipulable manmade objects because they have typical forms and shapes that makes them recognizable. The form of a chess object is not directly related to its function but the form and function are firmly coupled through chess rules (e.g., how certain pieces move). The functions are in turn inextricably linked to actions, that is, movements associated with chess objects (e.g., executing a move).

Most importantly, the game of chess enables us to compare chess experts, who possess extensive experience and knowledge about chess objects and their relations, with chess novices, who are superficially familiar with the game of chess and its objects. This expertise approach features falsification in the experimental design [33]–[35] and thus should provide insight in the neural mechanism behind object recognition. Of particular interest is to see how the well-known object recognition network mediates experts' chess specific recognition in comparison to that of novices. Skilled recognition may, for example, engage the same left lateral areas known to be engaged in non-skilled recognition. The same areas would, however, work more or less in terms of increased or decreased neural firing rates to accommodate experience based differences between skilled and non-skilled recognition. In this case, we would assume that skilled recognition involves qualitatively similar processes as non-skilled recognition. The difference would be of a quantitative nature [23], [36]–[37]. Alternatively, the processes of skilled recognition may involve additional areas in the same, or even in the other, hemisphere to meet processing demands. In this case, we would assume that skilled recognition is not only a more efficient version of non-skilled recognition, but that it also involves qualitatively different processes.

We investigated the recognition processes of 1) neutral geometrical shapes (Control task), 2) chess objects (Identity task) and 3) functions of chess objects (Check task – see Figure 1A for all three tasks) in expert and novice chess players using behavioral (reaction time and eye movement recordings) and neuroimaging techniques. The Control task involved recognition of geometrical objects because it is reasonable to assume that both expert and novice chess players have the same degree of expertise (most likely rather limited expertise) with geometrical shapes. In contrast, the Identity task required the domain-specific object recognition which should favour experts who possess knowledge about chess pieces (e.g., form, function). Comparing the Identity with Control task will thus enable us to pinpoint behavioral and neural mechanism underlying chess-specific object recognition. The Check task involved object recognition similarly as the Identity task because it is necessary to recognize the chess piece to determine whether it is checking the king. The Check task also required an additional component related to the function of the identified object, that is, the possible moves of this certain piece. The comparison between Check and Control tasks should identify not only object recognition, but also its coupling with the explicit retrieval of objects' functions. The retrieval of function and the process of relating two objects will be identified by comparing Check with Identity task. Finally, the comparison between experts and novices on the chess-specific tasks enabled us to identify the neural basis of skilled chess-specific recognition of objects and their functions.