Groupitizing Improves Estimation of Numerosity of Auditory Sequences

Anobile G., Castaldi E., Maldonado Moscoso P. A., Arrighi R., Burr D.

Groupitizing is a recently described phenomenon of numerosity perception where

clustering items of a set into smaller “subitizable” groups improves discrimination.

Groupitizing is thought to be rooted on the subitizing system, with which it shares several

properties: both phenomena accelerate counting and decrease estimation thresholds

irrespective of stimulus format (for both simultaneous and sequential numerosity

perception) and both rely on attention. As previous research on groupitizing has been

almost completely limited to vision, the current study investigates whether it generalizes

to other sensory modalities. Participants estimated the numerosity of a series of tones

clustered either by proximity in time or by similarity in frequency. We found that

compared with unstructured tone sequences, grouping lowered auditory estimation

thresholds by up to 20%. The groupitizing advantage was similar across different

grouping conditions, temporal proximity and tone frequency similarity. These results

mirror the groupitizing effect for visual stimuli, suggesting that, like subitizing, groupitizing

is an a-modal phenomenon.