Small-range numerical representations of linguistic sounds in 9- to 10-months-old infants

• In Event: Poster Session 07
  In Poster Session: PS 07 Topic - Cognitive Processes

Abstract

Very young infants readily discriminate visual displays on the basis of the numerical information (e.g. Izard et al., 2009). However, the capacity to precisely represent the number of items in memory seems limited to one item at around 5 months of age (e.g. Káldy & Leslie, 2005) and to about 3 items/chunks by 10-12 months (e.g. Feigenson et al., 2002). This capacity has been considerably less studied in the auditory domain. A few studies using habituation paradigms have shown that 6 (vanMarle & Wynn, 2009) and 9 month-old infants (Lipton & Spelke 2004) fail to differentiate 2 from 3 tone sequences, which could be taken as a first indication of the limits in infants’ auditory numerical representations.

The aim of the present study was to further investigate this capacity with a focus on linguistic materials. Thus, different from previous studies, the ability to represent sets over syllables (not tones) and to generalize this property to different sets was tested.

Study Population
Participants were 9 to 10 months-old infants (Exp 1. N=18, N males = 9; Exp 2. N=20, N males = 10; Exp 3. N=16, N males = 8). All participants were full term, with no birth complications, and no hearing or visual problems reported.

Methods
The experiment consisted of a Learning phase of 20 trials and a test phase of 8 trials. In the learning trials, we taught infants to look to one side of the screen (right or left) when a sequence with a given number of syllables was presented (e.g. 2 syllables), and to look to the other side when another set of syllables (e.g. 3 syllables) was presented. A looming puppet appeared after each syllable sequence, on the corresponding side. The test trials were similar to the familiarization trials, except that no puppet appeared after each syllable sequence and new syllable sets were presented (See Fig. 1). Infants’ gaze was recorded with an eye-tracker (TOBII 1750), and the first fixation was coded as correct or incorrect based on the correspondence with the pairing sequence-side learned during the familiarization phase. We computed difference scores and separate t-test to compare the scores to chance level.

Results
The results indicate that infants distinguished and separately represented 2 and 3 syllable-sets both when the syllable sequences differed in the overall duration (Exp. 1; p < 0.01; d’ = 0.589) and when edited to have identical duration (Exp. 2; p < 0.05; d’ = 0.52). In Experiment 3 infants failed to distinguish 3 and 4 syllable-sets (p = 0.45; d’ = 0.19). See Figure 2.

Conclusions
The results suggest that capacity limits within the infant auditory memory system might vary depending on the nature of the stimuli. The greater capacity for holding syllables might be associated with the infants’ preference to listening to speech from the earliest stages of development (e.g. Vouloumanos & Werker, 2007).

Authors

• Silvia Benavides-Varela, Università degli Studi di Padova (UNIPD)
  Presenting Author

• Natalia Reoyo-Serrano, Università degli Studi di Padova (UNIPD)
  Non-Presenting Author