The symmetry-induced numerosity illusion depends on visual attention

Area of Science:

• Cognitive Psychology
• Visual Perception
• Neuroscience

Background:

• Symmetry is a fundamental visual cue for organizing scenes and object segmentation.
• Symmetry can, however, lead to perceptual biases, notably underestimating quantities in symmetric arrays.
• The underlying mechanisms of this symmetry-induced numerosity underestimation remain unclear.

Purpose of the Study:

• To investigate if attentional resources influence the underestimation of quantities in symmetric visual arrays.
• To determine the role of perceptual grouping mechanisms, dependent on attention, in this bias.

Main Methods:

• Twenty-six adults performed numerosity judgments on symmetric and random dot arrays.
• Participants completed tasks under single-task (ignoring distractor) and dual-task (judging distractor color/orientation) conditions to manipulate attentional load.
• The effect of attentional diversion on symmetry-induced numerosity underestimation was measured.

Main Results:

• The symmetry-induced underestimation of numerical quantities was significantly reduced when attentional resources were diverted.
• Halving the attentional resources available halved the magnitude of the numerosity bias.
• This suggests that attentional resources play a crucial role in the perception of symmetric arrays.

Conclusions:

• The bias in perceiving quantities within symmetric arrays is, at least partially, dependent on attentional resources.
• The findings suggest that attentional-dependent grouping mechanisms may underlie the symmetry-induced numerosity underestimation.
• Understanding these attentional effects is key to comprehending visual biases in quantity perception.