Several physiologically oriented studies have also revealed lateral hemifield attentional asymmetries. These studies suggest that the left cortical hemisphere mediates attention to the RVF while the right cortical hemisphere mediates attention to both the LVF and RVF (Badzakova-Trajkove et al.,
2010; Heilman & Van Den Abell,
1980; Mesulam,
1981; Nobre et al.,
1997; Szczepanski, Konen, & Kastner,
2010; Vandenberghe et al.,
1997).
6 It is intriguing, then, that all of the present distractor-induced impairments occurred only when participants attended targets in the RVF—which is presumably monitored by
both hemispheres. To appreciate this counterintuitive point, consider current thinking about another attentional hemifield asymmetry, the lower (versus upper) hemifield attentional advantage (He, Cavanagh, & Intriligator,
1996; Lakha & Humphreys,
2005).
7 He et al. (
1996) have explained this lower field attentional advantage by noting that the parietal lobe—an attention related region (Buschman & Miller,
2007)—receives more projections from the lower than the upper hemifield (Van Essen, Newsome, & Maunsell,
1984). Enhanced lower hemifield visual performance also correlates retinotopically with enhanced fMRI activity patterns in early visual cortical areas (Liu, Heeger, & Carrasco,
2006), which impose an important constraint on visual attention (Carlson, Alvarez, & Cavanagh,
2007). Extending this reasoning, the presumed RVF representation in both cortical hemispheres would seemingly predict greater (not less) distractor immunity in the RVF than in the LVF—opposite to the present findings. Perhaps there are important
qualitative differences between the neural resources mediating attention to the left versus right hemifields. In fact, experimental manipulations involving EEG (Verleger et al.,
2009) and transcranial magnetic stimulation (Müri et al.,
2002; Woo, Kim, & Lee,
2009) coupled with clinical reports of split brain (Forster, Corballis, & Corballis,
2000) and right parietal lobe patients (Battelli et al.,
2001; Battelli, Cavanagh, Martini, & Barton,
2003; Rorden, Mattingley, Karnath, & Driver,
1997) suggest that the right parietal lobe is specialized for temporal judgments. Such findings have led to recent speculation about a “when” pathway (Battelli, Pascual-Leone, & Cavanagh,
2007; Battelli, Walsh, Pascual-Leone, & Cavanagh,
2008; Davis, Christie, & Rorden,
2009) that is distinct from the “what” (ventral) and “where” (dorsal) pathways (Mishkin & Ungerleider,
1982). The task- and hemifield-specific error patterns in our
Experiment 1 provide further evidence that distinct neural events set the limit on temporal versus spatial judgments.