Abstract

Abstract

The study of the neural basis of consciousness is relatively novel compared to other scientific pursuits. Due to the complexity of the problem, many researchers in the field have adopted a simplified approach in which the initial goal is to identify neural correlates of basic conscious experiences, such as seeing a picture. Various techniques are now available to present an identical visual stimulus that is sometimes consciously seen and other times unconsciously processed by the visual system. By contrasting these two carefully controlled conditions, it is possible to isolate brain activity associated with conscious perception while keeping sensory input constant. Based on this method, two main categories of theories have arisen: “sensory theories” and “cognitive theories” of consciousness. Such theories make distinct predictions about the timing and neuroanatomical locations of the neural correlates of conscious vision. To test these theories, the proposed study uses a “no-report paradigm” along with electroencephalogram (EEG) recordings to isolate neural activity related to conscious vision from neural activity related to reporting what one has just seen. We expect to find that a brainwave previously thought to index conscious perception (P3b) is in fact a signifier of reporting an experience; not of having the experience. Such a result would challenge cognitive theories and support sensory theories of consciousness. Alternatively, if we find the P3b wave in the no-report condition, cognitive theories would be supported. This general line of research has implications for basic science, clinical detection of consciousness in patients, and diagnosis/treatment of disorders of consciousness.

Abstract

Abstract

Grapheme-color synesthesia is a condition in which affected individuals experience consistent associations between graphemes (letter or numbers) and colors. In previous research done at Reed College’s SCALP Lab it was found that, compared with control participants, people with grapheme-color synesthesia had shorter response times (RTs) and shorter latency and larger amplitude N2pc in a visual search task using achromatic displays (black graphemes on white background). The N2pc is a well-known neural marker of selective attention. These findings suggested that synesthetes were using their experience of color to guide their attention and speed up their visual search. To confirm this, a second experiment showed that control participants presented with colored vs. achromatic graphemes show a similar advantage to that observed in synesthetes vs. controls. However, there is still the possibility that synesthetes may have a general advantage in speed of processing that is independent of their synesthetic color experience. The current proposal seeks to investigate whether the observed synesthetic advantage in visual search tasks extends to stimuli other than English graphemes. Synesthetes and non-synesthetes will perform a visual search task in three conditions: Georgian graphemes (unfamiliar graphemes), stick figures (non-graphemes), and English graphemes (familiar graphemes). The expected result is that synesthetes will only show an advantage (shorter RT and earlier/larger N2pc) in the familiar grapheme condition. This result would demonstrate that the synesthetic advantage is due to the color-grapheme associations formed with familiar graphemes and not to another undefined ability of synesthetes to perform better on any visual search task.

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Abstract

This study intended to investigate the nature of processing of multiple adjectives via the recording of brain activity elicited by sentences containing contradictory sequences that appear to violate grammatical-semantic constraints (e.g. “the small big dog chased the ball”). In a prior study using similar sentences, Kemmerer et. al. (2007) found a reduced N400 and an enhanced P600 at the 2nd adjective (e.g. big) proposing that these effects reflect semantic and syntactic aspects of a temporary reanalysis. Our study tested this proposal by presenting 3 types of contexts containing high, low, or no licensing information prior to the critical sentence. If Kemmerer et. al. are correct, we proposed that the P600 and N400 effects should disappear or decrease considerably when sentences follow licensing (high information) contexts. In contrast, if the effects remained, alternative accounts based on a syntactic-semantic reanalysis would be supported. Our study also introduced a broader range of adjective types than Kemmerer et al., to explore whether the N400/P600 effects are a general effect of contradictory adjectives or whether this is an effect of the relative interpretation of dimension adjectives (e.g. big/small).

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Abstract

Abstract

Abstract

Abstract

Previous studies have suggested that linguistic information is processed differently from non-linguistic sounds at early and late stages of auditory perception; however, the neural mechanisms responsible for discrimination between speech and non-speech sounds have been notoriously difficult to identify due to the physical acoustic differences between speech and non-speech stimuli.  Sine-wave speech (SWS) is a unique auditory phenomenon in which the same physical stimulus can be perceived as noise or as speech depending on perceptual expectations.  In this study we compared event-related potentials (ERPs) elicited by SWS stimuli in both non-speech and speech conditions. Participants completed a discrimination task between four SWS sounds before and after they had been trained to hear the sounds as speech.  We found that the N1 auditory component was larger in the non-speech condition, likely reflecting increased attentional demands for the more difficult task of sound discrimination compared to speech discrimination.  The speech and non-speech elicited ERPs also diverged around 300 ms over the frontal scalp, resulting in a lasting positive shift in the speech condition compared to the non-speech condition.  This latter difference may reflect upper-level speech processes.  Follow-up studies controlling for task difficulty and word repetition will also be discussed.

Abstract

Current theories of monolingual language comprehension suggest that phonological processing precedes semantic information, which in turn precedes syntactic information.  Bilingual language comprehension likely requires an additional level: knowledge of which language a specific word belongs to.  The Revised Bilingual Interactive Activation (BIA+) model of word recognition proposes that bilinguals use language ‘tags,’ that is, information identifying the specific language of a word, to help them monitor the appropriate language of use at any given time (Dijkstra & van Heuven, 2002).  A central question then is when exactly this language ‘tag’ information becomes available during language comprehension.  Using the recording of event-related potentials, we investigated the time course of semantic and language ‘tag’ encoding during visual word recognition.  Spanish-English bilinguals viewed a series of printed words while making dual-choice go/nogo and left/right hand decisions based on semantic (whether the word was an object or an animal) and language ‘tag’ information (whether the word was in English or Spanish).  According to initial findings, the onset latency of the N200 (a component related to response inhibition) indicated that language ‘tag’ information may be accessed as early as semantic information or soon after. This finding is compatible with the BIA+ model, supporting the claim that language ‘tag’ information is accessed relatively late (i.e. compared to phonological information) during bilingual word recognition. That is, the language ‘tag’ information may come too late to filter out words inappropriate to the current language context.