Prosimian primates show ratio dependence in spontaneous quantity discriminations

Area of Science:

• Comparative Psychology
• Cognitive Neuroscience
• Primatology

Background:

• Previous research suggests human infants and some animals use an object file system for small quantities, not the approximate number system (ANS).
• This implies a limited capacity for numerical processing in certain contexts.
• The distinction between these systems is crucial for understanding numerical cognition evolution.

Purpose of the Study:

• To directly test the predictions of the ANS and object file system in prosimian primates.
• To investigate spontaneous numerical judgments in prosimians using controlled food choice tasks.
• To differentiate between object-tracking and quantity-discrimination mechanisms in non-human primates.

Main Methods:

• Prosimian primates were presented with sequential food choices between two baited buckets.
• Comparisons involved varying quantities to contrast ANS and object file system predictions.
• Ratios tested included 1:3, 1:2, and 2:3, across small (≤3) and large (>3) quantities.

Main Results:

• Prosimians consistently selected the larger quantity when the ratio was 1:3, irrespective of quantity size.
• Discrimination was not robust for a 1:2 ratio across conditions.
• No preference was shown for small quantities with a 2:3 ratio.

Conclusions:

• The findings implicate the approximate number system (ANS) in prosimian spontaneous numerical discriminations.
• Results challenge the notion that only object file systems are engaged for small quantities in primates.
• This study provides evidence for ANS-based numerical processing in non-human primates.