Does a Flatter General Gradient of Visual Attention Explain Peripheral Advantages and Central Deficits in Deaf Adults?

Abstract

Individuals deaf from early age often outperform hearing individuals in the visual periphery on attention-dependent dorsal stream tasks (e.g., spatial localization or movement detection), but sometimes show central visual attention deficits, usually on ventral stream object identification tasks. It has been proposed that early deafness adaptively redirects attentional resources from central to peripheral vision to monitor extrapersonal space in the absence of auditory cues, producing a more evenly distributed attention gradient across visual space. However, little direct evidence exists that peripheral advantages are functionally tied to central deficits, rather than determined by independent mechanisms, and previous studies using several attention tasks typically report peripheral advantages or central deficits, not both. To test the general altered attentional gradient proposal, we employed a novel divided attention paradigm that measured target localization performance along a gradient from parafoveal to peripheral locations, independent of concurrent central object identification performance in prelingually deaf and hearing groups who differed in access to auditory input. Deaf participants without cochlear implants (No-CI), with cochlear implants (CI), and hearing participants identified vehicles presented centrally, and concurrently reported the location of parafoveal (1.4°) and peripheral (13.3°) targets among distractors. No-CI participants but not CI participants showed a central identification accuracy deficit. However, all groups displayed equivalent target localization accuracy at peripheral and parafoveal locations and nearly parallel parafoveal-peripheral gradients. Furthermore, the No-CI group's central identification deficit remained after statistically controlling peripheral performance; conversely, the parafoveal and peripheral group performance equivalencies remained after controlling central identification accuracy. These results suggest that, in the absence of auditory input, reduced central attentional capacity is not necessarily associated with enhanced peripheral attentional capacity or with flattening of a general attention gradient. Our findings converge with earlier studies suggesting that a general graded trade-off of attentional resources across the visual field does not adequately explain the complex task-dependent spatial distribution of deaf-hearing performance differences reported in the literature. Rather, growing evidence suggests that the spatial distribution of attention-mediated performance in deaf people is determined by sophisticated cross-modal plasticity mechanisms that recruit specific sensory and polymodal cortex to achieve specific compensatory processing goals.

Keywords: attention; central deficit; cochlear implant; cross-modal plasticity; deafness; peripheral advantage.

FIGURE 1

Sample stimuli and trial structure. On each trial, a fixation point (^∗) lasting 500 ms was replaced by a central vehicle target or non-target flanked by a localization target (X) and three distractors (O) for 100 ms, followed by a blank screen for an inter-trial interval (ITI) of 2 s. Central vehicle targets were either cars or non-cars. Probability of a central vehicle target or non-target appearing on a given trial was 0.5. Probability of a localization target X appearing at any one of the eight parafoveal or peripheral locations on a given trial was 0.125. Vehicle category (car vs. non-car) was perfectly balanced across localization target location. Sample vehicle images are taken from the POPORO set (Kovalenko et al., 2012). Stimuli in figure are not drawn to scale.

FIGURE 2

Percent accuracy for central vehicle identification task targets (centered at 0° eccentricity) and for parafoveal (1.4°) and peripheral (13.3°) localization task targets. Localization gradients for each group are represented by the straight lines connecting the data points between parafoveal and peripheral locations. These lines represent the piecewise slope determined by sparse sampling at two discrete eccentricities along the performance gradients for each group. They are not intended to imply accurately interpolated values at intermediate eccentricities that were not sampled in our study or to reflect any assumption that the attentional gradient between those sampled eccentricities is strictly linear for any group. CI: deaf cochlear implant group; No-CI: deaf group without cochlear implants; Hearing: hearing group. Error bars are standard errors for the hearing group (thick bars) and for the No-CI group (thin bars). ^∗No-CI vs. Hearing Group planned comparison, p < 0.035.