Pupillometry as a test of infant word recognition

By 11 months of age, infants recognize commonly occurring word forms in their environment. The Head Turn Preference Paradigm (HTPP) is the one method of measuring infant word form recognition. The HTPP uses looking times as judged by a head turn of the infant towards or away from a speaker. This method is thus subject to infant attention, which can make it difficult to get accurate results when infants are not paying attention due to external factors (for example, teething). Pupillometry is a non-invasive, physiological measurement that uses pupil dilation to assess cognitive processes. Pupil dilations have been found to be an accurate measurement of cognitive load in infants because pupil dilations reflect involuntary activity in the nervous system. Therefore, pupillometry is a non-behavioral assessment of infant word form recognition that may provide richer data than the HTPP. This Honors project was a pilot study for a larger study. The larger study assesses infant word form recognition through pupil dilations and head turns using a common form of the HTPP called the One Screen Head Turn Preference Test. This Honors project compares the results of pupillometry and the One Screen Head Turn Preference Test in one infant from the larger study. It makes a direct comparison of the two methodologies to determine if they can be used side by side to assess infant behavior. PUPILLOMETRY AS A TEST OF INFANT WORD RECOGNITION 4 Pupillometry as a Test of Infant Word Recognition The process of developing language is very complex because of the different components of language such as form (sounds, words, and word order), content (meaning of words), and use (social communication). One of the ways researchers understand language acquisition during the first few years of life is by studying infants’ word form recognition at various ages (Halle & Boysson-Bardies, 1994). Word form recognition differs from word recognition since it does not imply meaning, only recognition of the sounds forming the words. When infants recognize word forms they do so without any context clues. For example, infants do not need to be looking at a ball or playing with a ball to recognize the word form of ball (DePaolis, Keren-Portnoy, & Vihman, 2016). Once researchers know how infants recognize word forms they can explore other aspects of language, such as how words are stored in infants’ brains and what aspects of stress are necessary for infants to recognize words (Halle & Boysson-Bardies, 1996; Swingley, 2005; Vihman, Nakai, DePaolis, & Halle, 2004). By developing an understanding of infant language acquisition, researchers also become aware of the typical pattern of language development. This then allows researchers to pay particular attention to infants whose language does not seem to be following the typical language development pattern (Owens, 2013). It is important to identify infants who show atypical language development because infants who receive early intervention for a language disorder have better chances of acquiring language skills similar to typically developing infants (Owens, 2013). In order to test infants’ word form recognition, simple, non-invasive measures must be used because infants are a fragile population (Sirois & Brisson, 2014). Since the 1980s, the most common and successful method of measuring the cognitive process of word form recognition in PUPILLOMETRY AS A TEST OF INFANT WORD RECOGNITION 5 infants has been the Head Turn Preference Paradigm (HTPP). The HTPP is a non-invasive, behavioral assessment that uses the length of time infants look toward a sound source to determine infants’ word form recognition (DePaolis et al., 2016). There are a few detractors to using the HTPP though. For example, the HTPP is subject to human error and it is reliant on infants’ behavior, which can be influenced by outside factors (DePaolis et al., 2016; Jusczyk & Aslin, 1995). Pupillometry is a non-invasive, physiological assessment of pupil dilation that may be able to resolve some of the problems associated with the HTPP (Hepach & Westermann, 2016; Sirois & Brisson, 2014; Sirois & Jackson, 2012; Yeung, Denison, & Johnson, 2016). For the past 50 years, pupillometry has shown that adults’ pupils dilate in response to their processing of information (Beatty, 1982; Sirois & Brisson, 2014). So far, only a few studies have used pupillometry to study language processing skills in infants (Hochmann & Papeo, 2014). This Honors project is a part of a larger study that investigated infants’ pupil dilation as a measure of recognizing familiar word forms. There is evidence for a connection between word form recognition and pupil dilation from the results of many studies that show pupil dilation reflects cognitive load in adults and infants (Beatty, 1982; Hepach & Westermann, 2016; Jackson & Sirois, 2009; Sirois & Jackson, 2012). The larger study used a common form of the HTPP called the One Screen Head Turn Preference Test. This served as a parallel measure to pupillometry that assessed concurrent validity (data from one test matches that of a previously established measurement of the same construct). This Honors project was a pilot study that compared the use of pupillometry and the One Screen Head Turn Preference Test in one 13month-old infant from the larger study. It makes a direct comparison of the two methodologies PUPILLOMETRY AS A TEST OF INFANT WORD RECOGNITION 6 being explored to provide insight into whether these two methods can be used simultaneously to reflect the onset of word form recognition. Background Familiarity vs. Novelty Preference The foundation upon which many experimental techniques for assessing infant development is infants’ preference for both novel and familiar stimuli. It was originally proposed that infants older than two months of age preferred novel stimuli (Hunter & Ames, 1988). However, it was realized that preferences are not linked to age but are linked to task difficulty and familiarization time. As familiarization time increases, infants shift from no preference to a familiarity preference to a novelty preference (Hunter & Ames, 1988). Thus, infants prefer both familiar and novel stimuli. The model developed by Hunter & Ames (1988) has been adapted for use in many different studies. One such study examined infant familiarly and novelty responses to words at lexical onset (DePaolis et al., 2016). It found that infants who had no preference for stimuli were less phonetically advanced than infants who showed a familiarity or novelty preference. The study also concluded that infants who had a novelty preference had a better understanding of the words presented than infants who had a familiarity or no preference. Thus, familiarity, novelty, and no preference reveal different aspects of development in infants’ expression and comprehension (DePaolis et al., 2016). Head Turn Preference Paradigm (HTPP) For the past 21 years, infant word form recognition has been primarily measured using the Head Turn Preference Paradigm (HTPP; Halle & Boysson-Bardies, 1996). The HTPP is a suitable method for testing infants’ word form recognition because of their tendency to turn PUPILLOMETRY AS A TEST OF INFANT WORD RECOGNITION 7 towards a sound source, especially when motivating stimulation depends on their head turns (Nelson, Jusczyk, Mandel, Myers, Turk, & Gerken, 1995). In the HTPP, infants are seated on a parent’s lap in a testing booth (Nelson et al., 1995). One loudspeaker hangs from each of the two side walls with an attached blinking red light. A blinking green light is placed in the center panel and used to orient the infants’ attention to the center. Once the infants’ attention is centered, the green light is shut off and one of the red lights on the side wall is initiated. When the infants’ attention is perceived to be on the red light, a prerecorded, randomized list of familiar or rare words is presented through the speaker. Researchers stop playing the stimulus when the infants look away for at least two consecutive seconds (DePaolis et al., 2016; Halle & Boysson-Bardies, 1994; Halle & Boysson-Bardies, 1996; Jusczyk & Aslin, 1995; Nelson et al., 1995; Swingley, 2005; Vihman et al., 2004). Researchers use two buttons to indicate where infants are looking during the HTPP. To begin trials, one button is pressed to indicate that infants are looking toward the center. The other button is pressed when infants turn their heads at least 30° toward the sound source until they look away (Nelson et al., 1995; Vihman et al., 2004). It is important that researchers are unaware of the stimulus being played to avoid any bias in determining looks towards the center or away. Thus, researchers wear earplugs or headphones to prevent them from hearing stimuli. Often a video camera is used to record test sessions so that reliability checks can be performed (Nelson et al., 1995). The results of the HTPP consistently reveal that 11-month-old infants turn their heads for a longer amount of time when familiar words are presented (DePaolis et al., 2016; Halle & Boysson-Bardies, 1994; Halle & Boysson-Bardies, 1996; Jusczyk & Aslin, 1995; Swingley,