BITTSy can run conditioned headturn studies, a paradigm in which the child is trained (or conditioned) to turn a particular direction when they hear a particular event or a change in an event. Conditioned headturn can be used to test children's hearing (for audiometry - turn when a sound is heard), or can be used to test discrimination (turn when a change in a repeated sequence of sounds occurs). For the original use of this paradigm, see Eilers, Wilson & Moore, 1977; or see Kuhl , 1985 or Polka, Jusczyk & Rvachew, 1995, for methodological reviews.
In conditioned headturn studies, the child is seated on their parent's lap facing an assistant; the assistant maintains the infant's attention forward by playing silently with toys. Test trials consist of an auditory stimulus - either the presence of a sound, or a change in a background sound.
During training, the test trials are especially salient or obvious (a large change, or a loud sound). Immediately afterwards, a reinforcer then turns on to the side of the infant - originally, this was a lit-up animatronic toy, but it can be anything that would reward (and encourage) a child to look to that side. This reward plays briefly, and then turns off, so that the infant's gaze returns to the assistant, and the process repeats.
After a series of trials, the infant learns to expect that the reward will occur whenever the sound change happens. At this point, the reward itself is gradually delayed relative to the event, such that the infant begins to turn BEFORE the reward happens, or to anticipate it. This is the response that the experimenter is looking for - a turn towards the reinforcer when the particular sound occurs (before the reinforcer), rather than a turn in response to the reinforcer. There is a preset criterion for the test phase to end (e.g., three correct anticipatory head turns).
At this point, training ends, and the test phase begins; the experimenter indicates when a child is ready, and the computer randomly selects either a change trial (where the sound changes) or a control (no-change) trial, where the sound does not change. The experimenter indicates when the child turns his or her head; this leads to 4 potential trial results: a hit (the sound did change, and the infant turned appropriately), a miss (the sound changed but the infant did not turn), a false positive (the child turned even though there was no sound change), or a correct rejection (there was no change, and the child did not turn). These are then used to determine a child's discrimination ability. Only hits are reinforced during this test phase.
An alternative form of conditioned headturn uses two distinct reinforcers, and the infant is trained to turn either to the left or to the right. Other studies add a generalization phase after the standard test phase.
Creating conditioned headturn studies in BITTSy was made possible with the addition of the JUMP command in version 1.5. Due to its later introduction, implementing conditioned headturn paradigm is currently a bit "clunkier" than the other main paradigms BITTSy was designed to run, and the process of developing these protocols is typically more complex. While BITTSy can execute the typical trial and phase structures of conditioned headturn, there are some types of phase progression logic used in prior studies that are difficult to replicate exactly in BITTSy. However, similar to headturn preference procedure, the use of conditioned headturn has been limited by the unavailability of a standard system capable of running these procedures. The ability of BITTSy to run these paradigms provides an easy way for researchers to begin using this paradigm. We hope that BITTSy will allow more labs to adopt and adapt this paradigm for their research.
BITTSy was designed to allow testing using the Headturn Preference Procedure, a paradigm for which there are no other freely-available standardized test systems. Below we discuss the way HPP works, and some of its advantages.
Since the time it was first developed in the early 1980s (Colombo & Bundy, 1981; Fernald, 1985), the HPP has been a cornerstone method for studying early language development, and has been used in several of the most influential studies in infant speech perception (e.g., Fernald, 1985; Jusczyk & Aslin, 1995; Saffran, Aslin, & Newport, 1996, collectively cited more than 1000 times). The last substantial modifications to the method were made in the mid 1990s (Jusczyk & Aslin, 1995; Kemler Nelson et al., 1995) and current set-ups have lagged behind advances in software programming and hardware. In the standard variant, infants sit on their caregivers’ laps in a 3-walled test booth (see Fig. 3). Based on an observer's real-time coding of infant orienting behavior, a computer controls flashing lights, one on each wall of the booth, and 2 audio speakers, one under each of the side lights. Typically, trials begin with the light in front of the infant flashing, attracting the infant’s attention front and center. After the infant orients to the center, the light stops flashing and one of the two side lights begins to flash. When the infant turns towards that light, sounds begin to play from the speaker on that side; sounds continue until the sound file ends or until the infant looks away for a pre-determined amount of time (usually 2 seconds), ending the trial. By comparing infant orientation and attention to trials of different types, researchers can examine the types of sounds and sound patterns infants recognize, differentiate, or prefer. Although some studies have used HPP to test infants’ ability to discriminate between different stimuli (e.g.Nazzi et al., 2000), its most common use is to test either infants’ recognition of stimuli or their preference for specific components of their native language (see Johnson & Zamuner, 2010 for a recent review). When combined with a familiarization or training phase, this paradigm not only examines what children have already learned about their language(s), but also provides information as to what they are able to learn in the laboratory (Marcus et al., 1999; Saffran et al., 1996).
HPP uses infants’ natural tendency to maintain visual orientation towards an attended sound source
The task puts minimal demands on the infants as compared to tasks that require children to understand verbal instructions and produce an overt reaching or verbal response.
This makes HPP ideal for separating differences in perceptual skills from differences in the comprehension or processing of verbal instructions.
HPP is easy to use across a wide age-range that includes key milestones of language development.
HPP has been used with typically-developing children ranging from 4 months (see, for example, Mandel et al., 1995; Seidl, Cristià, Bernard, & Onishi, 2009) through 2 years (Santelmann & Jusczyk, 1998; Tincoff, 2006), a perfect range for examining early language development.
A unique quality of HPP is that it provides opportunities to study developmental change through cross-sectional and longitudinal studies; use of the same task across ages helps to ensure that changes are the result of cognitive/perceptual development rather than differences in task difficulty.
HPP is extremely flexible.
HPP can be used with stimuli ranging in complexity from single syllables (e.g. McMurray & Aslin, 2005) to entire passages (Jusczyk & Aslin, 1995; Soderstrom & Morgan, 2007), and with both speech and nonspeech stimuli.
HPP has been used to examine long term memory for sound patterns presented in the lab (Houston & Jusczyk, 2003) and from naturalistic settings (Jusczyk & Hohne, 1997; Saffran, Loman, & Robertson, 2000), and to explore musical knowledge and learning (Krumhansl & Jusczyk, 1990; Saffran & Griepentrog, 2001; Saffran et al., 2000), rule learning (Marcus et al., 1999), auditory stream segregation (Newman, 2005), and knowledge of phonetic categories (McMurray & Aslin, 2005), phonotactics (Chambers, Onishi, & Fisher, 2003, in press; Jusczyk et al., 1993), and prosody (Seidl & Cristià, 2008).
HPP maximizes research resources, compared to other infant testing procedures.
Sessions last approximately 10-15 minutes, which is well-matched to the attention spans of infants in the target age range. Shorter sessions maximize the number of infants who are able to complete the experimental session and provide usable data. Low attrition rate is particularly important when testing populations for whom recruitment can be difficult and costly, such as bilingual or atypical infants.
Observer training can be effectively accomplished in a relatively short period of time, thus maximizing research assistants’ time for collecting and analyzing data.
The original use of the HPP paradigm focused on typically-developing monolingual infants in the 4-12 month age range, and there are still relatively few speech perception studies with bilingual infants using HPP (e.g., Bosch & Sebastián-Gallés, 2001; Bosch & Sebastián-Gallés, 2003; Vihman et al., 2007). Although most research using HPP focuses on infants under one year of age, recent work has demonstrated the use of HPP in typically-developing infants in the 20-24-month age range and in clinical populations with children as old as 48 months (c.f., Soderstrom & Morgan, 2007; Van Heugten & Johnson, 2010). Research has also demonstrated links between early listening preferences shown through HPP and subsequent linguistic and cognitive development (Newman, Bernstein Ratner, Jusczyk, Jusczyk, & Dow, 2006). Researchers are also starting to use behavioral paradigms in concert with physiological measures, such as heart-rate and ERPs (Kooijman, Johnson, & Cutler, 2008; Panneton & Richards, under review), and have begun developing visual variants of HPP for testing American Sign Language (Baird, Seal, & DePaolis, 2010). All of these point to new ways to use this paradigm with other populations.
One limitation of previous research with HPP is that the majority of this research has used flashing lights as the primary attention-getting device, and flashing lights may not hold the attention of more cognitively-advanced participants, such as older children. Recent studies have begun showing images on flat screen monitors (Bosch & Sebastián-Gallés, 2001; Volkova, Trehub, & Schellenberg, 2006), an extension that lends itself well to testing older children in that it creates a more visually stimulating environment. BITTSy is designed to allow either the use of traditional lights, or the use of video monitors; if your test room is set up with both, you can switch between them just by what you list in your protocol file (that is, you do not need to set up your system to do one or the other; it can be set up to allow both.)
Until BITTSy was developed, there was no easily available, off-the-shelf testing system for HPP. HPP was dependent upon custom-designed hardware – the computer needed to be physically connected to the test booth as well as to an input panel which researchers use to indicate the direction in which infants orient. The input panel required specialized wiring, and response boxes needed to be created specifically for each research lab. Most researchers using HPP had to employ their own programmer and electrical engineering consultants to build the system. This limited the use of the approach to only individuals with substantial funding and technical resources and more importantly, it reduced the likelihood of new investigators implementing this methodology.
Since most researchers developed their own systems, there was no standardization, making cross-site collaborative research very difficult. This in turn limited comparative work across populations located in distinct geographical areas (e.g., work comparing infants with different language exposure). This was particularly problematic for research examining the role of different language combinations in infants raised bilingually, in that few locales have easy access to sufficiently large populations of infants raised in particular types of households.
Finally, at the time that BITTSy was created, many of the systems in use were becoming obsolete, as the timing boards and software tied to specific operating systems.
In addition to HPP, BITTSy also allows testing using the Preferential Looking Paradigm (Golinkoff, Ma, Song, & Hirsh-Pasek, 2013). During this procedure, children are presented with pairs of images (or animated objects) on a screen. This can include familiar (e.g., a hand) or unfamiliar items (e.g., an object that the child would not know the label for). Sometimes the objects are presented one at a time (e.g., during familiarization and training), and sometimes they appear in pairs or in groups of 4 images. Images are accompanied by speech stimuli, which may include sentences either teaching children a new word, or instructing them to look at one of the objects on the screen. A digital camera positioned near the screen (typically above or below) records children’s eye movements. Videos of the test-sessions are then coded off-line on a frame-by-frame basis by trained research assistants, to measure participants' fixations and to calculate accuracy and reaction times across trials.
Visual fixation is a type of habituation paradigm frequently used to study either infant auditory or visual discrimination. The Switch paradigm (Stager & Werker, 1997) is one type of visual fixation procedure.
In visual fixation, the infant is facing a central video screen which shows an image on each trial; at the same time, a sound is played. The infant's interest in the auditory stimulus is measured by how long they choose to look at the co-occuring visual image.
In most cases, the image is not intended to represent the sound; for example, the child might see a bullseye image, or a checkerboard, paired with a repeating sound (such as a syllable). At first, the image and sound are novel, so the infant attends for a fair amount of time. But as the trial repeats over and over, the combination of sound plus image eventually become less interesting, and the child's attention level drops. This is referred to as habituation; it is usually defined experimentally in terms of a set decrease in attention (e.g., looking 50% of the time as at the start of the study).
In BITTSy, the habituation criteria can be based on a percentage decrease from initial looking (e.g., the first 3 trials), or from peak looking (the 3 trials with longest average looking). You can also set the amount of decrease in looking (e.g., 50%, 60%) and the number of trials over which looking is averaged.
The Switch paradigm is a form of VFP in which infants are first "taught" one or two new words and then tested on their learning of that pairing. During the habituation phase, they are presented with a particular combination of auditory word and visual image. After habituation, the child is then presented with either the same pairing, or a "switch". For example, if the child was habituated with object A + sound 1 and object B + sound 2, they would be tested with either a correct pairing (object A + sound 1) or a switch (ojbect B + sound 1). If children have learned the specific pairing, they should dishabituate (or increase their looking) to the novel pairing.
See the habituation section for more information about setting up visual fixation/habituation studies in BITTSy.