Voluntary attention improves performance similarly around the visual field

Abstract

Performance as a function of polar angle at isoeccentric locations across the visual field is known as a performance field (PF) and is characterized by two asymmetries: the HVA (horizontal-vertical anisotropy) and VMA (vertical meridian asymmetry). Exogenous (involuntary) spatial attention does not affect the shape of the PF, improving performance similarly across polar angle. Here we investigated whether endogenous (voluntary) spatial attention, a flexible mechanism, can attenuate these perceptual asymmetries. Twenty participants performed an orientation discrimination task while their endogenous attention was either directed to the target location or distributed across all possible locations. The effects of attention were assessed either using the same stimulus contrast across locations or equating difficulty across locations using individually titrated contrast thresholds. In both experiments, endogenous attention similarly improved performance at all locations, maintaining the canonical PF shape. Thus, despite its voluntary nature, like exogenous attention, endogenous attention cannot alleviate perceptual asymmetries at isoeccentric locations.

Keywords: Contrast sensitivity; Endogenous attention; Horizontal-vertical anisotropy; Spatial vision; Vertical meridian asymmetry; Visual performance fields.

Fig. 1. Schematic representation of a typical visual performance field.

The center point (intersection of the cardinal lines) represents chance performance and more eccentric points represent higher performance. (1) Horizontal-vertical anisotropy (HVA): better performance at isoeccentric locations along the horizontal (left horizontal meridian (LHM) and right horizontal meridian (RHM) locations) than vertical (upper vertical meridian (UVM) and lower vertical meridian (LVM) locations) meridian of the visual field, and (2) vertical meridian asymmetry (VMA), better performance at the location directly below fixation (LVM) than directly above (UVM).

Fig. 2. Task sequence.

(a) Observers performed a two-alternative forced-choice (2AFC) orientation discrimination task, contingent upon contrast sensitivity, while maintaining fixation. The target could appear at any one of four isoeccentric locations along the cardinals. Participants were either cued towards a single location (Valid cue) or to all four locations (Neutral cue). On every trial, four Gabor patches briefly appeared simultaneously at all stimulus locations. A response cue indicated the target, for which participants reported the tilt (left or right). Note that Gabor tilt angle, size of placeholders, fixation point, and response cue have been exaggerated for clarity. Subpanel: Group average stimulus contrast by location was the same for valid and neutral cue condition trials in each experiment, and are shown for (b) Experiment 1, same contrast across locations resulting in different performance across locations, and (c) Experiment 2, different contrast at different locations to equate performance across locations.

Fig. 3. Performance in Experiment 1.

Green - valid cue condition trials, blue - neutral cue condition trials. (a) Average d’ for each location (polar plot of performance field). (b) Scatterplot of individual d’ values of the horizontal-vertical anisotropy (HVA) (average d’ at horizontal meridian (HM) vs. average d’ at vertical meridian (VM)). (c) Scatterplot of individual d’ values of the vertical meridian asymmetry (VMA) (average d’ at lower vertical meridian (LVM) vs. average d’ at upper vertical meridian (UVM)). (d) Group average d’ (bar plots overall and by location). (e) Group average median reaction times (bar plots overall and by location). Error bars are ±1 SEM. n.s. = not significant; *p < .05; **p < .01; ***p < .001.

Fig. 4. Correlations between conditions across locations in Experiment 1.

Correlations between participants’ performance in the neutral and attention conditions across locations – horizontal meridian (HM; red dots), lower vertical meridian (LVM; yellow dots) and upper vertical meridian (UVM; orange dots)

Fig. 5. Performance in Experiment 2.

Green - valid cue condition trials, blue - neutral cue condition trials. (a) Average d’ for each location (polar plot of performance field). (b) Scatterplot of individual d’ values of the horizontal-vertical anisotropy (HVA; average d’ at horizontal meridian (HM) vs. average d’ at vertical meridian (VM)). (c) Scatterplot of individual d’ values of the vertical meridian asymmetry (VMA; average d’ at lower vertical meridian (LVM) vs. average d’ at upper vertical meridian (UVM). (d) Group average d’ (bar plots overall and by location). (e) Group average median reaction times (data points overall and by location). Error bars are ±1 SEM. n.s. = not significant; *p < .05; **p < .01; ***p < .001.