Given that neural resources are limited outside central vision (Adams & Horton,
2002,
2003; Horton & Hoyt,
1991; Inouye,
1909; Lister & Holmes,
1916), it should not be surprising to observe averaging of features in parafoveal and peripheral visual areas (e.g., Greenwood, Bex, & Dakin,
2009,
2010; Parkes, Lund, Angelucci, Solomon, & Morgan,
2001). Averaging in the periphery has been primarily attributed to mechanisms associated with crowding, a visual phenomenon whereby signals of surrounding stimuli can crowd out signals of a single target, therefore, preventing and/or interfering with its identification and recognition (Bouma,
1970, also see Levi,
2008, and Pelli & Tillman,
2008, for reviews). Although crowding effects have been extensively studied, from orientation identification of artificial stimuli (e.g., Greenwood et al.,
2009,
2010; Parkes et al.,
2001) to feature discriminations in natural scenes (e.g., To, Gilchrist, Troscianko, Kho, & Tolhurst,
2009; To, Gilchrist, Troscianko, & Tolhurst,
2011), its underlying mechanisms remain largely speculative, and theories do not always reflect the known behavior of neurons. A few neurophysiological studies of V1 have compared single neurons with peripheral and central (cat) or foveal (primate) receptive fields. Generally, it has been found that peripheral neurons have larger receptive fields and respond to corresponding lower spatial frequencies of grating (Hubel & Wiesel,
1974; Tolhurst & Thompson,
1981; H. H. Yu et al.,
2010). These findings may explain how simple visual acuity falls off with increasing eccentricity, but only subtle differences between foveal and peripheral neural processing have been reported in V1 (H. H. Yu & Rosa,
2014), and these do not seem to explain phenomena, such as veneer acuity or crowding (Levi, Klein, & Aitsebaomo,
1985). Although it used to be well accepted that cortical magnification factors were closely related to retinal sampling density and receptive field size (e.g., Hubel & Wiesel,
1974), many studies since have reported that foveal V1 is greatly enlarged, even allowing for its smaller receptive fields (Adams & Horton,
2003; Popovic & Sjöstrand,
2001; Tolhurst & Ling,
1988). This implies that foveal neural processing has more dimensions than peripheral, but this finding is not an explanation for crowding or the poverty of peripheral visual perception. We are not aware of any single neuron studies that explicitly investigate responses with stimulus paradigms that cause crowding in human perception. Nonetheless, the effects of crowding have been successfully modeled by spatial uncertainty and substitution (Freeman, Chakravarthi, & Pelli,
2012; Krumhansl & Thomas,
1977; Nandy & Tjan,
2007; Pelli,
1985; Põder & Wagemans,
2007; Popple & Levi,
2005; Strasburger,
2005; Wolford,
1975), imprecise integration (Neri & Levi,
2006; van den Berg, Roerdink, & Cornelissen,
2010), limited field of view (Tjan,
2009), and averaging (also referred to as signal pooling; Freeman et al.,
2012; Greenwood et al.,
2009,
2010; Parkes et al.,
2001) in behavioral studies.