Werker et al. (1981)

Tested three groups of subjects:

1. English-speaking adults
2. Hindi-speaking adults
3. Twelve "English-hearing" infants (6-8 months)

Subjects had to discriminate the following pairs:

1. /ba/ vs. /ga/
2. /ta/ vs. /ta/
3. /t^ha/ vs. /d^ha/

Infants went through a "head turn" task and adults simply pressed a button.

Results:

1. Hindi speakers discriminated all contrasts
2. Infant listeners discriminated all contrasts.
3. English speakers could only discriminate /ba/ - /da/.

(But with training, English speakers showed some success in discriminating the Hindi contrasts.)

When do infants start losing non-native perceptual contrasts?

Werker and Tees (1984)

Tested infants at:

1. 6-8 months
2. 8-10 months
3. 10-12 months

On non-native:

1. Hindi contrasts
2. Thompson contrasts /k^?i/ vs. /q^?i/

Study used a head-turn task.

Results:

1. All 6-8 month-old infants could discriminate the contrasts
2. Half of the 8-10 month-old infants could discriminate the contrasts
3. None of the 10-12 month-old infants could discriminate the contrasts

Conclusions:

1. Infants are born with an ability to categorically perceive any contrast in any of the world's languages.
2. By eight to ten months, infants lose this ability and can only discriminate contrasts in their native language.
3. Discrimination abilities are not completely lost but are "attenuated".