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.