Providing a first proof-of-principle for this idea, we have shown elsewhere (Gallivan et al.,
2011) that the immediate extraction of quantity information from nonsymbolic displays is intimately tied to the well-documented basic visual capacity of object enumeration or
parallel individuation (i.e., up to ∼ four items), a bottleneck often linked to our ability to distribute attention to multiple locations across space (Bays & Husain,
2008; Hyde & Spelke,
2011). The real-world observation that spatial attention appears closely coupled to overt action processes (e.g., eye movements, reaches, grasps, etc.) has prompted several theoretical frameworks to unite spatial attention and movement planning processes in the explanation of goal-directed motor behavior (Baldauf & Deubel,
2010; Bisley & Goldberg,
2010; Cisek & Kalaska,
2010; Moore, Armstrong, & Fallah,
2003; Rizzolatti, Riggio, Dascola, & Umilta,
1987). Several variants of this general framework argue that behaviorally relevant objects in our environment compete in parallel for action selection, forming complex
attentional landscapes or
salience maps with hills of neural activity forming at the locations of these objects in space (Bisley & Goldberg,
2010; Fecteau & Munoz,
2006; Gottlieb,
2002; Gottlieb, Kusunoki, & Goldberg,
1998). Perhaps not coincidentally, the types of location maps proposed by theories of nonsymbolic magnitude processing and implemented by the neuronal models (Dehaene & Changeux,
1993; Verguts & Fias,
2004) look like and function very similarly to the location maps denoting objects of behavioral relevance, as used by the theoretical frameworks that unite spatial attention and movement planning processes. Taken together, it seems quite likely that this basic parallel individuation system, and by extension the numerical processing of nonsymbolic items, may be evolutionarily rooted in the more primitive mechanisms that support rapid reflexive motor planning and behavior (see also Dehaene & Changeux,
1993, for a similar suggestion). This notion is in line with the basic capacities of nonsymbolic numerical processing (i.e., up to ∼ four items) observed in semifree-ranging monkeys (Hauser, Carey, & Hauser,
2000) and preverbal infants (Feigenson et al.,
2004), who both lack symbol manipulation capabilities. In contrast, it is clear that symbolic number processing and manipulation requires far more advanced cognitive mechanisms (e.g., additional top-down connections) allowing the formation of more abstract associations (via prefrontal cortex, see Nieder,
2009; Nieder & Dehaene,
2009) and perhaps also the development (or evolution) of distinct brain areas in the human visual system (Shum et al.,
2013), both of which are not likely to fall within the evolutionary purview of early visuomotor structures.