Inconsistent flanker congruency effects across stimulus types and age groups: A cautionary tale.

The flanker task is a common measure of selective attention and response competition across populations, age groups, and experiential contexts. Adapting it for different uses often involves changing methodological features that are rarely empirically compared with the previous design. This paper presents an example of how typical methodological changes can differentially elicit congruency effects across age groups. We compared two flanker tasks, using direction stimuli on a laptop versus color stimuli on a tablet, in young children (2-7 years; Experiment 1), older children (6-10 years; Experiment 2a), and adults (19-23 years; Experiment 2b). Young children showed the expected congruency effects in the direction task, and one year later a subset of the sample completed the color task, also showing congruency effects. Longitudinal comparisons showed no difference in the congruency effect across tasks, but nearly half of the sample was excluded due to high error rates. To avoid excluding children with few correct trials, we modified a new measure, signed residual time, to incorporate correctness and reaction time per trial. With the larger sample, this measure showed no difference in congruency effects across tasks. To compare these tasks when completed within the same session, we tested older children and young adults in both tasks and found congruency effects in the direction task but not the color task. These results raise concern that tasks adapted for young children may not perform comparably in other samples, and we caution researchers to anticipate this possibility when modifying cognitive tasks.

Four-month-old infants' visual investigation of cats and dogs: relations with pet experience and attentional strategy.

We assessed the eye-movements of 4-month-old infants (N = 38) as they visually inspected pairs of images of cats or dogs. In general, infants who had previous experience with pets exhibited more sophisticated inspection than did infants without pet experience, both directing more visual attention to the informative head regions of the animals, particularly when comparing stimuli, and maintaining their attention to an individual animal, resisting the pull on their attention by the other visible animal. Individual differences in general attentional strategies as assessed during a pretest had similar but weaker relations to visual scanning patterns. There was some evidence that the 2 factors were interactively associated with visual inspection, supporting the findings of Kovack-Lesh and colleagues (Kovack-Lesh, Horst, & Oakes, 2008; Kovack-Lesh, Oakes, & McMurray, 2012) that infants' learning about and memory for this type of stimuli is jointly determined by pet experience and attentional style.

Infant directed speech and the development of speech perception: enhancing development or an unintended consequence?

Infant directed speech (IDS) is a speech register characterized by simpler sentences, a slower rate, and more variable prosody. Recent work has implicated it in more subtle aspects of language development. Kuhl et al. (1997) demonstrated that segmental cues for vowels are affected by IDS in a way that may enhance development: the average locations of the extreme "point" vowels (/a/, /i/ and /u/) are further apart in acoustic space. If infants learn speech categories, in part, from the statistical distributions of such cues, these changes may specifically enhance speech category learning. We revisited this by asking (1) if these findings extend to a new cue (Voice Onset Time, a cue for voicing); (2) whether they extend to the interior vowels which are much harder to learn and/or discriminate; and (3) whether these changes may be an unintended phonetic consequence of factors like speaking rate or prosodic changes associated with IDS. Eighteen caregivers were recorded reading a picture book including minimal pairs for voicing (e.g., beach/peach) and a variety of vowels to either an adult or their infant. Acoustic measurements suggested that VOT was different in IDS, but not in a way that necessarily supports better development, and that these changes are almost entirely due to slower rate of speech of IDS. Measurements of the vowel suggested that in addition to changes in the mean, there was also an increase in variance, and statistical modeling suggests that this may counteract the benefit of any expansion of the vowel space. As a whole this suggests that changes in segmental cues associated with IDS may be an unintended by-product of the slower rate of speech and different prosodic structure, and do not necessarily derive from a motivation to enhance development.

Infants' Visual Recognition Memory for a Series of Categorically Related Items.

We examined the interactions between visual recognition memory, working memory, and categorization by examining 6-month-old infants' (N = 168) memory for individual items in a categorized list (e.g., images of dogs or cats). In Experiments 1 and 2, infants were familiarized with 6 different cats or dogs, presented one at a time on a series of 15-s familiarization trials. When the test occurred immediately after the sixth familiarization trial (Experiment 1), infants showed strong novelty preference for items presented on the fourth or fifth familiarization trial, but not for the items presented on the first three trials or on the sixth trial. When a brief (15-s) retention delay occurred between the end of the sixth trial and the test trials (Experiment 2), memory for the sixth item was enhanced, memory for the fourth item was impaired, and memory for the fifth was unchanged relative to when no retention delay was included. Experiment 3 confirmed that infants can form a memory for the first item presented. These results reveal how factors such as interference and time to consolidate influence infants' visual recognition memory as they categorize a series of items.

Contributions of attentional style and previous experience to 4-month-old infants' categorization.

We examined how infants' categorization is jointly influenced by previous experience and how much they shift their gaze back-and-forth between stimuli. Extending previous findings reported by Kovack-Lesh, Horst, and Oakes (2008), we found that 4-month-old infants' (N = 122) learning of the exclusive category of cats was related to whether they had cats at home and how much they shifted attention between two available stimuli during familiarization. Individual differences in attention assessed in an unrelated task were not related to their categorization. Thus, infants' learning is multiply influenced by past experience and on-line attentional style.

The influence of pets on infants' processing of cat and dog images.

We examined how experience at home with pets is related to infants' processing of animal stimuli in a standard laboratory procedure. We presented 6-month-old infants with photographs of cats or dogs and found that infants with pets at home (N=40) responded differently to the pictures than infants without pets (N=40). These results suggest that infants' experience in one context (at home) contributes to their processing of similar stimuli in a different context (the laboratory), and have implications for how infants' early experience shapes basic cognitive processing.

Two are better than one: comparison influences infants' visual recognition memory.

Despite a large literature on infants' memory for visually presented stimuli, the processes underlying visual memory are not well understood. Two studies with 4-month-olds (N=60) examined the effects of providing opportunities for comparison of items on infants' memory for those items. Experiment 1 revealed that 4-month-olds failed to show evidence of memory for an item presented during familiarization in a standard task (i.e., when only one item was presented during familiarization). In Experiment 2, infants showed robust memory for one of two different items presented during familiarization. Thus, infants' memory for the distinctive features of individual items was enhanced when they could compare items.

Hold your horses: how exposure to different items influences infant categorization.

We investigated how exposure to pairs of different items (as compared with pairs of identical items) influences 10-month-olds' (n=79) categorization of horses versus dogs in an object-examining task. Infants responded to an exclusive category when familiarized with pairs of different items but not when familiarized with pairs of identical items (Experiment 1), even when the frequency of exposure to each item was controlled (Experiment 2). When familiarized with pairs of identical items, infants failed to show evidence of memory for the individual exemplars (Experiment 3). Reducing the retention interval between presentations of different items in the identical pairs condition facilitated infants' recognition of an exclusive categorical distinction (Experiment 4). These results are discussed in terms of how exposure to collections of different items, and how opportunities to compare items, influences infants' categorization.