Knowledge that Transforms

Accumulated evidence from electrophysiology and neuroimaging suggests that face perception involves extrastriate visual mechanisms specialized in processing physiognomic features and building a perceptual representation that is categorically distinct and can be identified by face-recognition units. In the present experiment, we recorded event-related brain potentials in order to explore possible contextual influences on the activity of this perceptual mechanism. Subjects werefirst exposed to pairs of small shapes, which did not elicit any face-specific brain activity. The same stimuli, however, elicitedface-specific brain activity after subjects saw them embedded in schematic faces, which probably primed the subjects to interpret the shapes as schematic eyes. No face-specific activity was observed when objects rather than faces were used to form the context. We conclude that the activity of face-specific extrastriate perceptual mechanisms can be modulated by contextual constraints that determine the significance of the visual input.

Visual attention enables observers to extract and process high-priority information in the visualfield. Controversy remains as to whether or not observers can ignore information that falls within the spatial beam of attention. We used an objective physiological measure, the steady-state visual evoked potential (SSVEP), to investigate this question. A stream of flickering small, uppercase letters was embedded in the center of a stream of large, uppercase letters. A unitary beam would result in no difference of the SSVEP amplitude elicited by the small letter stream when it was attended versus ignored (i.e., when subjects attended the large letter stream). Contrary to this prediction, SSVEP amplitude increased by almost 100% when the small letter stream was attended compared with when it was ignored. The results support the notion that the attentional spotlight can be formed like a doughnut, processing central information differentially depending on whether it is attended or ignored.

Recognizing spoken language involves automatic activation of multiple candidate words. The process of selection between candidates is made more efficient by inhibition of embedded words (like egg in beg) that leave a portion of the input stranded (here, b). Results from European languages suggest that this inhibition occurs when consonants are stranded but not when syllables are stranded. The reason why leftover syllables do not lead to inhibition could be that in principle they might themselves be words; in European languages, a syllable can be a word. In Sesotho (a Bantu language), however, a single syllable cannot be a word. We report that in Sesotho, word recognition is inhibited by stranded consonants, but stranded monosyllables produce no more difficulty than stranded bisyllables (which could be Sesotho words). Thisfinding suggests that the viability constraint which inhibits spurious embedded word candidates is not sensitive to language-specific word structure, but is universal.

Are age differences in source memory inevitable? The two experiments reported here examined the hypothesis that the type of source information being tested mediates the magnitude of age differences in source memory. In these studies, participants listened to statements made by two different speakers. We compared younger and older adults' source memory in a traditional perceptual source task (memory for voice) and in two affective, conceptually based source tasks (truth of the statements, character of a person in a photo). In both studies, the perceptual and conceptual source information were conveyed in the same manner, as one speaker was associated with one type of information (e.g., female voice speaks truth). Age differences were robust for decisions regarding who said each statement but were negligible or truth or character decisions. These findings are provocative because they suggest that the type of information can influence age-related patterns of performance for source-conveyed information.

We examined children's ability to translate their preverbal memories into language following a period of substantial language development. Children participated in a unique event, and their memory was assessed 6 months or 1 year later. At the time of the event and at the time of the test, their language skills were also assessed. Children of all ages exhibited evidence of verbal and nonverbal memory. Their language skills also improved over the delay. By the time of the test, children of all ages had acquired most of the vocabulary necessary to describe the target event. Despite this, they did not translate preverbal aspects of their memory into language during the test. In no instance did a child verbally report information about the event that was not part of his or her productive vocabulary at the time of encoding. We conclude that language development plays a pivotal role in childhood amnesia.

The degree to which infants represent phonetic detail in words has been a source of controversy in phonology and developmental psychology. One prominent hypothesis holds that infants store words in a vague or inaccurate form until the learning of similar-sounding neighbors forces attention to subtle phonetic distinctions. In the experiment reported here, we used a visual fixation task to assess word recognition. We present the first evidence indicating that, infact, the lexical representations of 14- and 15-month-olds are encoded in fine detail, even when this detail is not functionally necessary for distinguishing similar words in the infant's vocabulary. Exposure to words is sufficient for well-specified lexical representations, even well before the vocabulary spurt. These results suggest developmental continuity in infants' representations of speech: As infants begin to build a vocabulary and learn word meanings, they use the perceptual abilities previously demonstrated in tasks testing the discrimination and categorization of meaningless syllables.