Association between synesthetic colors and sensitivity to physical colors changed by type of synesthetic experience in grapheme-color synesthesia

Grapheme-color synesthesia is a condition in which visual perception of letters induces simultaneous perception of a specific color. Previous studies indicate that grapheme-color synesthetes are more sensitive to physical colors than non-synesthetes. Synesthetic colors are found to be concentrated in multiple regions of the color space, forming “synesthetic color clusters”. The present study investigated whether color sensitivity corresponding to synesthetic color clusters (clustered colors) is higher than color sensitivity that does not correspond to synesthetic color clusters (non-clustered colors). However, we found no difference in the color sensitivity for clustered and non-clustered colors. We also investigated whether the color sensitivity is dependent on the synesthetic experience (associators and projectors). We found that the greater the tendency toward associator characteristics, the greater the sensitivity for clustered colors compared to that for non-clustered colors. Our findings suggest an association between synesthetic colors and physical color sensitivity that is modulated by synesthetic experience.     

Bright sneezes and dark coughs, loud sunlight and soft moonlight

Synesthetic metaphors (such as "the dawn comes up like thunder") are expressions in which words or phrases describing experiences proper to one sense modality transfer their meanings to another modality. In a series of four experiments, subjects used scales of loudness, pitch, and brightness to evaluate the meanings of a variety of synesthetic (auditory-visual) metaphors. Loudness and pitch expressed themselves metaphorically as greater brightness; in turn, brightness expressed itself as greater loudness and as higher pitch. Although loudness thus shared with brightness a metaphorical connection, pitch and brightness showed a connection that was closer and that applied more generally to different kinds of visual brightness. The ways that people evaluate synesthetic metaphors emulate the characteristics of synesthetic perception, thereby suggesting that synesthesia in perception and synesthesia in language both may emenate from the same source-from a phenomenological similarity in the makeup of sensory experiences of different modalities.     

The interaction of synesthetic and print color and its relation to visual imagery

Synesthetic color induced by graphemes is well understood to be an automatic perceptual phenomenon paralleling print color in some ways, but also differing in others. We addressed this juxtaposition by asking how synesthetes are affected by synesthetic and print colors that are the same. We tested two groups of grapheme–color synesthetes using a basic color-priming method in which a grapheme prime was presented, followed by a color patch (probe), the color of which was to be named as quickly and accurately as possible. The primes induced either no color, print color only, synesthetic color only, or both forms of color (e.g., a letter “A” printed in red that also triggered synesthetic red). As expected, responses to name the probe color were faster if it was congruent with the prime color than if it was incongruent. The new finding (Exp. 1) was that a prime that induced the same print and synesthetic colors led to substantially larger priming effects than did either type of color individually, an effect that could not be attributed to semantic priming (Exp. 2). In addition, the synesthesia effects correlated with a standard measure of visual imagery. These findings are discussed as being consistent with the hypothesis that print and synesthetic color converge on similar color mechanisms.     

Consistency in synesthetic experience to vowels and consonants: Five case studies

The present study attempted to specify the actual degree of consistency in synesthetic experience in two synesthetes and three non-synesthetes. By comparing colour chip selections, and size and density ratings, to the same set of stimulus letters on separate occasions, it was found that the synesthetic subjects showed a high consistency in responding over a short (24 hours) as well as a long (one year) time span. In comparison, the non-synesthetic subjects demonstrated less consistent responding when retested after 24 hours. However, the differences between the two groups were smaller than expected. Consistency to vowels and consonants was compared, and it was found that consistency to consonants was comparable to, or even higher than, vowel consistency in all subjects.     

The influence of synesthesia on eye movements: no synesthetic pop-out in an oculomotor target selection task

Recent research on grapheme-colour synesthesia has focused on whether visual attention is necessary to induce a synesthetic percept. The current study investigated the influence of synesthesia on overt visual attention during an oculomotor target selection task. Chromatic and achromatic stimuli were presented with one target among distractors (e.g. a ‘2’ (target) among multiple ‘5’s (distractors)). Participants executed an eye movement to the target. Synesthetes and controls showed a comparable target selection performance across conditions and a ‘pop-out effect’ was only seen in the chromatic condition. As a pop-out effect was absent for the synesthetes in the achromatic condition, a synesthetic element appears not to elicit a synesthetic colour, even when it is the target. The synesthetic percepts are not pre-attentively available to distinguish the synesthetic target from synesthetic distractors when elements are presented in the periphery. Synesthesia appears to require full recognition to bind form and colour.     

Executive functions in synesthesia

In grapheme-color synesthesia, a number or letter can evoke two different and possibly conflicting (real and synesthetic) color sensations at the same time. In this study, we investigate the relationship between synesthesia and executive control functions. First, no general skill differences were obtained between synesthetes and non-synesthetes in classic executive control paradigms. Furthermore, classic executive control effects did not interact with synesthetic behavioral effects. Third, we found support for our hypothesis that inhibition of a synesthetic color takes effort and time. Finally, individual differences analyses showed no relationship between the two skills; performance on a ‘normal’ Stroop task does not predict performance on a synesthetic Stroop task. Across four studies, the current results consistently show no clear relationship between executive control functions and synesthetic behavioral effects. This raises the question of which mechanisms are at play in synesthetic ‘management’ during the presence of two conflicting (real and synesthetic) sensations.     

Why Saturday could be both green and red in synesthesia

It has long been observed that certain words induce multiple synesthetic colors, a phenomenon that has remained largely unexplored. We report here on the distinct synesthetic colors two synesthetes experienced with closed sets of concepts (digits, weekdays, months). For example, Saturday was associated with green, like other word starting with s; however, Saturday also had its specific color (red). Auditory priming and Visual Color Stroop tasks were used to understand the cognitive mechanisms supporting the distinct synesthetic colors. Results revealed that processing of word segments and whole words was specifically involved in each type of synesthetic colors. However, these mechanisms differed between participants, as they could relate either to orthography (and written words) or phonology (and spoken words). Further differences concerned the word representations, which varied as to whether or not they encoded serial positions. In addition to clarifying the cognitive mechanisms underlying the distinct synesthetic colors, our results offer some clues for understanding the neurocognitive underpinnings of a rather common form of synesthesia.     

Consistency of synesthetic association varies with grapheme familiarity: A longitudinal study of grapheme-color synesthesia

Grapheme-color synesthesia is a condition in which the visual perception of letters or numbers induces a specific color sensation. The consistency of grapheme-color association has been considered as a fundamental characteristic of synesthesia. However, recent studies have indicated that this association can change across the adult lifespan, and it has become necessary to investigate the factors behind the changes within each synesthete. We conducted a longitudinal study of Japanese adult synesthetes to investigate long-term (5–8 years) changes in color responses to 300 graphemes (alphanumeric and Japanese characters). Graphemes with lower long-term consistency of synesthetic association also tended to have lower short-term consistency, indicating that grapheme-color association's consistency is determined for each grapheme. Further, less familiar graphemes had less consistent associations with their synesthetic colors. These findings suggest that a stronger grapheme-color association is formed for more familiar graphemes, leading to the consolidation of synesthetic color for such graphemes.     

No effect of synesthetic congruency on temporal ventriloquism

A sound presented in temporal proximity to a light can alter the perceived temporal occurrence of that light (temporal ventriloquism). Recent studies have suggested that pitch-size synesthetic congruency (i.e., a natural association between the relative pitch of a sound and the relative size of a visual stimulus) might affect this phenomenon. To reexamine this, participants made temporal order judgements about small- and large-sized visual stimuli while high- or low-pitched tones were presented before the first and after the second light. We replicated a previous study showing that, at large sound-light intervals, sensitivity for visual temporal order was better for synesthetically congruent than for incongruent pairs. However, this congruency effect could not be attributed to temporal ventriloquism, since it disappeared at short sound-light intervals, if compared with a synchronous audiovisual baseline condition that excluded response biases. In addition, synesthetic congruency did not affect temporal ventriloquism even if participants were made explicitly aware of congruency before testing. Our results thus challenge the view that synesthetic congruency affects temporal ventriloquism.     

Visual placing by human infants

Prior research has not agreed that extension of the arms by the human infant on approach to a surface is a visual response. In this research, human infants 8 to 11-months-old extended their arms on approach to a patterned surface covered with glass. The arms did not extend to a patterned surface 14 in. below the glass. Thus, the response is a visual, not a vestibular, proprioceptive one. Ambiguity of the visual stimulus that elicits the response is shown by the finding that the infants also extended their arms almost as much to a gray surface just beneath the glass as they did to the patterned one.     

Response discriminative and reinforcement factors in stimulus control of performance on multiple and chained schedules of reinforcement

Discriminative control of the response rates of two groups of rats was equated by training them to cease bar pressing in light-out no-tone ( + ) and to respond during tone and light. Multiple-schedule subjects received food at the same rate for responding during tone or light as for nonresponding in + . For the chained-schedule subjects responding in tone or light only produced + where food was received for nonresponding. In extinction tests multiple-schedule subjects emitted approximately twice the responses to tone-plus-light as to tone or light presented individually (additive summation). The rats trained on the chained schedule, in which the tone and light each controlled substantial response rates but were never paired with food, showed no summation when the tone and light were presented together. The results indicate that discriminative control of response rates and reinforcement differences between schedule components determine stimulus control.     

Second-order mappings in grapheme–color synesthesia

Typically, the search for order in grapheme–color synesthesia has been conducted by looking at the frequency of certain letter–color associations. Here, we report stronger associations when second-order similarity mappings are examined—specifically, mappings between the synesthetic colors of letters and letter shape, frequency, and position in the alphabet. The analyses demonstrate that these relations are independent of one other. More strikingly, our analyses show that each of the letter–color mappings is restricted to one dimension of color, with letter shape and ordinality linked to hue, and letter frequency linked to luminance. These results imply that synesthetic associations are acquired as the alphabet is learned, with associations involving letter shape, ordinality, and frequency being made independently and idiosyncratically. Because these mappings of similarity structure between domains (letters and colors) are similar to those found in numerous other cognitive and perceptual domains, they imply that synesthetic associations operate on principles common to many aspects of human cognition.     

Individual differences in aggressive responses to attack: Internal-external locus of control and field dependence-independence

Two experiments assessed the effect of individual differences on aggression. In both studies subjects were exposed to opponents in the competitive reaction time task who decreased the intensity of their attack from high to low, remained constantly moderate in their attack, or increased the intensity of their attack from low to high. In the first experiment Internal Locus of Control subjects consistently set high intensity shocks in response to high intensity attack and low shocks in response to mild attack. External subjects showed relatively minor variations in their aggressive responses to varying intensities of attack. In the second experiment field-independent subjects set more intense shocks than field-dependent subjects only in the Decreasing attack condition.     

The color of two alphabets for a multilingual synesthete

Interviews with a multilingual synesthete (MLS), who experiences colored letters for Roman and Cyrillic alphabets and for digits, revealed stable synesthetic experiences over 2 1/2 - 5 years. Colors of Cyrillic letters were based on Roman letters. Four Stroop tests involving both types of letters showed that MLS was able to name print color faster if the colors matched her synesthetic colors, showing that synesthesia is automatic. Letter-naming times for blocks of color were slower than those of actual letters, supporting unidirectionality of synesthesia. Stroop tests with Roman, but not Cyrillic, letters showed MLS acquired new temporary letter-color pairings and her color-naming times for these were not different from those for her original synesthetic colors.     

Database of synesthetic color associations for Japanese kanji

Synesthesia is a neurological phenomenon in which certain types of stimuli elicit involuntary perceptions in an unrelated pathway. A common type of synesthesia is grapheme–color synesthesia, in which the visual perception of letters and numbers stimulates the perception of a specific color. Previous studies have often collected relatively small numbers of grapheme–color associations per synesthete, but the accumulation of a large quantity of data has greater promise for uncovering the mechanisms underlying synesthetic association. In this study, we therefore collected large samples of data from a total of eight synesthetes. All told, we obtained over 1000 synesthetic colors associated with Japanese kanji characters from each of two synesthetes, over 100 synesthetic colors form each of three synesthetes, and about 80 synesthetic colors associated with Japanese hiragana, Latin letters, and Arabic numerals from each of three synesthetes. We then compiled the data into a database, called the KANJI-Synesthetic Colors Database (K-SCD), which has a total of 5122 colors for 483, 46, and 46 Japanese kanji, hiragana, and katakana characters, respectively, as well as for 26 Latin letters and ten Arabic numerals. In addition to introducing the K-SCD, this article demonstrates the database’s merits by using two examples, in which two new rules for synesthetic association, “shape similarity” and “synesthetic color clustering,” were found. The K-SCD is publicly accessible (www.cv.jinkan.kyoto-u.ac.jp/site/uploads/K-SCD.xlsm) and will be a valuable resource for those who wish to conduct statistical analyses using a rich dataset in order to uncover the rules governing synesthetic association and to understand its mechanisms.     

Superior encoding enhances recall in color-graphemic synesthesia

Synesthesia is a phenomenon in which particular stimuli, such as letters or sound, generate a secondary sensory experience in particular individuals. Reports of enhanced memory in synesthetes raise the question of its cognitive and neurological substrates. Enhanced memory in synesthetes could arise from the explicit or implicit use of a synesthetic cue to aid memory, from changes unique to the synesthete brain, or from both, depending on the task. To assess this question, we tested nine color-graphemic synesthetes using standardized neuropsychological measures that should not trigger color-graphemic synesthesia (visuo-spatial tests) and measures that should trigger color-graphemic synesthesia (verbal tasks). We found a synesthetic advantage on both types of tests, primarily in the initial encoding of information. The pattern of results adds to existing evidence of advantages in synesthetic memory, as well as provides novel evidence that synesthetes may have enhanced encoding rather than superior recall. Synesthetes learn more initially, rather than forgetting less over time.     

Multisensory synesthetic interactions in the speeded classification of visual size

In the present study, we attempted to demonstrate a synesthetic relationship between auditory frequency and visual size. In Experiment 1, participants performed a speeded visual size discrimination task in which they had to judge whether a variable-sized disk was bigger or smaller than a standard reference disk. A task-irrelevant sound that was either synesthetically congruent with the relative size of the disk (e.g., a low-frequency sound presented with a bigger disk) or synesthetically incongruent with it (e.g., a low-frequency sound presented with a smaller disk) was sometimes presented together with the variable disk. Reaction times were shorter in the synesthetically congruent condition than in the incongruent condition. Verbal labeling and semantic mediation interpretations of this interaction were explored in Experiment 2, in which high- and low-frequency sounds were presented in separate blocks of trials, and in Experiment 3, in which the tones were replaced by the spoken words "high" and "low." Response priming/bias explanations were ruled out in Experiment 4, in which a synesthetic congruency effect was still reported even when participants made same-versus-different discrimination responses regarding the relative sizes of the two disks. Taken together, these results provide the first empirical demonstration that the relative frequency of an irrelevant sound can influence the speed with which participants judge the size of visual stimuli when the sound varies on a trial-by-trial basis along a synesthetically compatible dimension. The possible cognitive bases for this synesthetic association are also discussed.     

Synesthetic perception and poetic metaphor

To explore the role of cross-modal perception in the apprehension of synesthetic metaphors, subjects read 15 short lines from poetry, each of which contained a metaphor relating visual and auditory qualities; the subjects' task was to set the loudness of a 1000-Hz tone and the brightness of a white light to match the levels implied by each metaphor. The sound settings and light settings suggest that a cross-modal equivalence between loudness and brightness largely underlay the responses to the metaphors. This general cross-modal equivalence was characterized by some notable intersubject differences and was modified, in part, by certain metaphors that resisted complete equivalence. Even so, the metaphorically induced settings of loudness and brightness are mainly governed by a cross-modality matching function that is qualitatively like the relation found in people with visual-auditory synesthesia, and that is quantitatively like the function obtained in more traditional psychophysical studies.     

Enhanced semantic priming in synesthetes independent of sensory binding

Synesthesia is the phenomenon in which individuals experience unusual involuntary cross-modal pairings. The evidence to date suggests that synesthetes have access to advantageous item-specific memory cues linked to their synesthetic experience, but whether this emphasis on item-specific memory cues comes at the expense of semantic-level processing has not been unambiguously demonstrated. Here we found that synesthetes produce substantially greater semantic priming magnitudes, unrelated to their specific synesthetic experience. This effect, however, was moderated by whether the synesthetes were projectors (their synesthetic experience occurs in their representation of external space), or associators (their synesthetic experience occurs in their ‘mind’s eye’). That is, the greater a synesthetes’s tendency to project their experience, the weaker their semantic priming when the task did not require them to semantically categorize the stimuli, whereas this trade-off was absent when the task did have that requirement.