The Aha! Moment: The Cognitive Neuroscience of Insight

ABSTRACT— A sudden comprehension that solves a problem, reinterprets a situation, explains a joke, or resolves an ambiguous percept is called an insight (i.e., the " Aha! moment"). Psychologists have studied insight using behavioral methods for nearly a century. Recently, the tools of cognitive neuroscience have been applied to this phenomenon. A series of studies have used electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) to study the neural correlates of the " Aha! moment" and its antecedents. Although the experience of insight is sudden and can seem disconnected from the immediately preceding thought, these studies show that insight is the culmination of a series of brain states and processes operating at different time scales. Elucidation of these precursors suggests interventional opportunities for the facilitation of insight.     

Left hemisphere sensitivity to consonant sounds not displayed by the right hemisphere: electrophysiological correlates

Auditory evoked responses (AER) to a series of consonant-vowel syllables were recorded from frontal, temporal, and parietal scalp locations from 14 right-handed college students. Averaged AERs were submitted to principal components analysis and analysis of variance. Six components of the group's AERs were found to reflect various aspects of the stimulus parameters. One component reflected changes over only the left hemisphere to different consonants. A second component changed systematically over both hemispheres but did not discriminate between all consonants.     

A factor related to the strength of an "Aha!" experience

Abstract: It is natural to assume that the strength of an "Aha!" becomes stronger when an unexpected solution is correct. In this study, this assumption is examined experimentally through a list of possible correct solutions. In the experiment, subjects listed the possible correct solutions before solving the problems, and evaluated the strength of their "Aha!" experience after they solved the problems. It was shown that the strength of the "Aha!" experience was strongest if the correct answer had not been included in the list of possible correct solutions; if included, the strength of the "Aha!" experience corresponded to the answer's position in the list, that is, the later the correct solution listed, the stronger the feeling became. It is suggested that the strength of an "Aha!" experience can be used as an error function in the learning process.     

Writing with the right hemisphere

We studied writing abilities in a strongly right-handed man following a massive stroke that resulted in virtually complete destruction of the language-dominant left hemisphere. Writing was characterized by sensitivity to lexical-semantic variables (i.e., word frequency, imageability, and part of speech), semantic errors in writing to dictation and written naming, total inability to use the nonlexical phonological spelling route, and agrammatism in spontaneous writing. The reliance on a lexical-semantic strategy in spelling, semantic errors, and impaired phonology and syntax were all highly consistent with the general characteristics of right hemisphere language, as revealed by studies of split-brain patients and adults with dominant hemispherectomy. In addition, this pattern of writing closely resembled the syndrome of deep agraphia. These observations provide strong support for the hypothesis that deep agraphia reflects right hemisphere writing.     

The right hemisphere maintains solution-related activation for yet-to-be-solved problems

In five experiments, we examined the time course of hemispheric differences in solution activation for insight-like problems. We propose that solving insight problems requires retrieval of unusual interpretations of problem elements, and that right-hemisphere (RH) coarse semantic coding is more likely than left-hemisphere (LH) fine semantic coding to maintain semantic activation of such interpretations. In four experiments, participants attempted word problems for 7 sec (Experiments 1A and 1B) or 2 sec (Experiments 2A and 2B), and 750 msec later responded to lateralized target words. After 7 sec of solving effort, Experiment 1A participants showed greater solution-related priming (i.e., they named solutions faster than unrelated words) for left visual field-RH (lvf-RH) targets than for right visual field-LH (rvf-LH) targets, and Experiment 1B participants made faster solution decisions on target words presented to the RH, as previously demonstrated following 15 sec of effort. After 2 sec of solving effort in Experiment 2A, women showed symmetric solution-related priming, although men showed a slight lvf-RH advantage in priming; and in Experiment 2B participants made equally quick solution decisions for targets presented to the LH and to the RH. In Experiment 3, participants viewed the problems for 1,250 msec then named lateralized target words; they showed symmetric solution-related priming. These experiments demonstrate solution activation initially in both hemispheres, but maintained solution activation only in the RH.     

Enhanced right hemisphere activation in the mathematically precocious: A preliminary EEG investigation

A preliminary electroencephalographic (EEG) investigation was conducted to determine if the pattern of hemispheric activation in mathematically precocious youth differs from that of average math ability subjects. Alpha activity at four brain sites (frontal, temporal, parietal, and occipital lobes) over the left and right cerebral hemispheres (LH/RH) was monitored while 12- to 14-year-old, right-handed males: (a) looked at a blank slide (baseline condition), (b) judged which of two chimeric faces was "happier," and (c) determined if a word was a noun or a verb. At baseline, the LH of the precocious group was found to be more active at all four brain sites relative to that of the average ability group. During chimeric face processing, the gifted subjects exhibited a significant reduction in alpha power over the RH, primarily at the temporal lobe, while no such alpha suppression was observed in the average ability subjects. For noun/verb determinations, no significant alpha power reductions were obtained for either group. These electrophysiological data generally corroborate the behavioral findings of O'Boyle and Benbow (1990a) and support their contention that enhanced RH involvement during cognitive processing may be a correlate of mathematical precocity. Moreover, the pattern of activation observed across tasks suggests that the ability to effectively coordinate LH and RH processing resources at an early age may be linked to intellectual giftedness.     

Probability matching in the right hemisphere

Previously it has been shown that the left hemisphere, but not the right, of split-brain patients tends to match the frequency of previous occurrences in probability-guessing paradigms (Wolford, Miller, & Gazzaniga, 2000). This phenomenon has been attributed to an "interpreter," a mechanism for making interpretations and forming hypotheses, thought to reside exclusively in the left hemisphere. In this study with a split-brain patient, we had him guess one of two types of faces, stimuli known to be preferentially processed in the right hemisphere of this patient. Unlike previous studies using other kinds of stimuli, the right hemisphere matched the frequency of the previous occurrences of a face-type, but the left hemisphere did not.     

Rhyming and the right hemisphere

Subjects determined whether two successively presented and orthographically different words rhymed with each other. The first word was presented at fixation and the second was presented either to the left or to the right of fixation, either alone (unilateral presentation) or accompanied by a distractor word in the other visual hemifield (bilateral presentation). Subjects were more accurate when the words did not rhyme, when presentation was unilateral, and when the target was flashed to the right visual hemifield. It was predicted that bilateral presentation would produce interference when information from both visual fields was processed by one hemisphere (callosal relay), but not when each of the two hemispheres performed a task independently (direct access). That is, callosal relay tasks should show greater laterality effects with bilateral presentations, whereas direct access tasks should show similar laterality effects with both bilateral and unilateral presentations. Greater laterality effects were observed for bilaterally presented rhyming words, but nonrhyming words showed similar laterality effects for both bilateral and unilateral presentations. These results suggest that judgment of nonrhyming words can be performed by either hemisphere, but that judgment of rhyming words requires callosal relay to the left hemisphere. The absence of a visual field difference with nonrhyming word pairs suggests further that judgment of nonrhyming word pairs may be accomplished by the right hemisphere when presentation is to the left visual field.     

The right hemisphere and temporal processing of consonant transition durations: electrophysiological correlates

Auditory evoked responses (AER) were recorded from frontal, temporal, and parietal scalp regions to a series of consonant-vowel syllables which varied in the duration of the consonant transition. Multivariate analyses of the AER waveforms identified one component of the AERs occurring only over right hemisphere regions which discriminated between differences in transition durations. A second component detected over only left hemisphere areas discriminated differences in place of articulation. These data are consistent with previous behavioral and electrophysiological reports that the right hemisphere is sensitive to temporal discriminations.     

Progressive dysfluency associated with right hemisphere disease

A late onset progressive dysfluency following a right hemisphere stroke occurred in a 62-year-old male. Dysfluency was characterized by pronounced word and phrase reiterations, and sound and syllable reiterations to a lesser degree. Spontaneous speech was significantly more dysfluent than oral reading and repetition. Recitation and singing were minimally dysfluent. Reiterations were accompanied by reduced vocal loudness and increased rate of speech. Reiterations occurred in initial, medial, and final sentence position. Secondary symptoms such as facial grimacing were absent. In contrast to acquired cortical stuttering which is characterized by a preponderance of sound and syllable sentence initial repetitions, dysfluency was more closely characteristic of palilalia. The dysfluency occurred as a symptom of a diffuse nonspecific subcortical projection system defect related to massive infarction in the right middle cerebral artery distribution with associated atrophy.     

Severe stuttering associated with right hemisphere lesion

Following a right hemisphere stroke, a right-handed, 50-year-old male experienced a permanent dysfluency characterized by phoneme and syllable reiterations and, to a lesser extent, word and phrase reiterations. The reiterations occurred in initial, medial, and final positions and for all sentence elements (e.g., subject nouns, object nouns, verbs, modifiers). There was a notable loss of verbal automatisms (poems, songs, etc.). The patient's symptoms conform to the acquired stuttering syndrome described by A. Helm, R. Butler, and D.F. Benson (1978, Neurology, 28, 1159-1165).     

Homotopic language reorganization in the right hemisphere after early left hemisphere injury

Speech production is inextricably linked to speech perception, yet they are usually investigated in isolation. In this study, we employed a verbal-repetition task to identify the neural substrates of speech processing with two ends active simultaneously using functional MRI. Subjects verbally repeated auditory stimuli containing an ambiguous vowel sound that could be perceived as either a word or a pseudoword depending on the interpretation of the vowel. We found verbal repetition commonly activated the audition-articulation interface bilaterally at Sylvian fissures and superior temporal sulci. Contrasting word-versus-pseudoword trials revealed neural activities unique to word repetition in the left posterior middle temporal areas and activities unique to pseudoword repetition in the left inferior frontal gyrus. These findings imply that the tasks are carried out using different speech codes: an articulation-based code of pseudowords and an acoustic-phonetic code of words. It also supports the dual-stream model and imitative learning of vocabulary.     

“啊哈！”和“哈哈！”：顿悟与幽默的脑认知成分比较

作为人类智能的高级表现形式, 顿悟和幽默存在诸多共同之处。从认知和情感组成上看, 顿悟的非连续性、突发性、重构和惊讶, 对应于幽默的失谐、失谐探测、失谐消解和愉悦, 两者存在表征机制的重叠。神经机制的研究发现, 顿悟和幽默的心理事件都伴随着400 ms左右的额中央区负波(N400)以及前扣带回、顶颞叶联合区和前额叶等脑区的活动; 同时顿悟和幽默在P300成分以及海马、右侧前部颞上回等脑区活动上存在差异。未来可借鉴幽默的认知和情感成份的脑成像研究范式, 进一步探明顿悟过程的认知和情感组成。     

Flexible contrast gain control in the right hemisphere

This study investigates whether the right hemisphere has more flexible contrast gain control settings for the identification of spatial frequency. Right-handed participants identified 1 and 9 cycles per degree sinusoidal gratings presented either to the left visual field-right hemisphere (LVF-RH) or the right visual field-left hemisphere (RVF-LH). When luminance contrast was randomized across a wide range (20-60%), performance gradually improved with contrast in the LVF-RH. Conversely, performance in the RVF-LH was disrupted and saturated for 20 and 60% of contrast, respectively, leading to a LVF-RH advantage for these contrast levels. When contrast was blocked or randomized for a smaller range (30-50%), the LVF-RH advantage was diminished. Flexible contrast gain control is needed when contrast is randomized across a wide range, but not when it is blocked or randomized across a smaller range. The results therefore suggest that the right hemisphere is able to process spatial frequency information across a wider range of contrast levels than is the left hemisphere.     

Neuropsychological syndromes in right hemisphere stroke patients

A specific set of syndromes, based on different intrahemispheric lesion locations, has not yet been described in patients with right hemisphere lesions. To explore whether statistically derived clusters could give clues to a syndrome structure, neuropsychological data from a sample of 106 patients with right hemisphere stroke were studied. CT data were available for 58 of the patients. Based on factor analysis of eight test and four ratings variables, six variables were chosen for a cluster analysis. A structure of 13 clusters was considered statistically valid. Combining clusters with parallel test profiles into main cluster classes, five right hemisphere syndromes proved clinically valid: an above average syndrome ( n =46), denial perseverance (frontal) syndrome ( n =14). a depressed mood syndrome ( n = 14), a focal RH syndrome ( n =18) and a global RH syndrome ( n =9). It is suggested that syndromes are related to intrahemispheric location of the lesion, such as the extent of anterior and posterior damage.     

Form-specific visual priming in the right cerebral hemisphere.

Results of 4 experiments indicate that both within-modality and case-specific visual priming for words are greater when test stimuli are presented initially to the right cerebral hemisphere (RH). In contrast, neither within-modality nor case-specific explicit memory for words is greater when stimuli are presented initially to the RH. Priming is measured using word-stem completion, and explicit memory is measured using word-stem cued recall. In both cases, Ss first rate how much they like words, and then word stems are presented briefly to the RH (in the left visual field) or to the left hemisphere (in the right visual field). Results suggest that at least 2 separate systems encode the visual representations that produce priming. The system that is more effective in the RH is better at representing form-specific information, whereas another system that is not more effective in the RH does not distinguish among distinct instances of word forms.