Tactual perception: a review of experimental variables and procedures <s> Blind participants <s> Three experiments compared congenitally blind and sighted adults and children on tasks presumed to involve visual imagery in memory. In all three, the blind subjects' performances were remarkably similar to the sighted. The first two experiments examined Paivio's (1971) modality-specific imagery hypothesis. Experiment 1 used a paired-associate task with words whose referents were high in either visual or auditory imagery. The blind, like the sighted, recalled more high-visual-imagery pairs than any others. Experiment 2 used a free-recall task for words grouped according to modality-specific attributes, such as color and sound. The blind performed as well as the sighted on words grouped by color. In fact, the only consistent deficit in both experiments occurred for the sighted in recall of words whose referents are primarily auditory. These results challenge Paivio's theory and suggest either (a) that the visual imagery used by the sighted is no more facilitating than the abstract semantic representations used by the blind or (b) that the sighted are not using visual imagery. Experiment 3 used Neisser and Kerr's (1973) imaging task. Subjects formed images of scenes in which target objects were described as either visible in the picture plane or concealed by another object and thus not visible. On an incidental recall test for the target objects, the blind, like the sighted, recalled more pictorial than concealed targets. This finding suggests that the haptic images of the blind maintain occlusion just as the visual images of the sighted do. Language: en <s> BIB001 </s> Tactual perception: a review of experimental variables and procedures <s> Blind participants <s> The study investigated the extent to which two groups of blind children were able to use tactual picture information to improve memory performance for auditorily presented texts. Adventitiously blind children demonstrated significant increases in amount recalled with illustrated presentation, showing improved recall of information represented in both the text and the picture. For congenitally blind children, the pictures also produced increased recall of pictorial information, but this was at the expense of recall of non-pictorial information represented in the text only. <s> BIB002 </s> Tactual perception: a review of experimental variables and procedures <s> Blind participants <s> A multi-stage sieve plate humidifier column with a series of plastic snap together modular mixing units that combine to form an elongated vertical column with interconnected mixing chambers. The column is confined inside a liquid supply bottle where it is submerged in a liquid used to humidify an inhalable gas such as oxygen or air. In a method of humidification, the gas is bubbled into a lower portion of the submerged column, transferred through the interconnecting chambers of the column where the bubbles are broken up and mixed with liquid, and then the humidified gas collected near a top of the column and conducted to a patient for inhalation. <s> BIB003 </s> Tactual perception: a review of experimental variables and procedures <s> Blind participants <s> Growing evidence suggests that blind subjects outperform the sighted on certain tactile discrimination tasks depending on cutaneous inputs. The purpose of this study was to compare the performance of blind (n = 14) and sighted (n = 15) subjects in a haptic angle discrimination task, depending on both cutaneous and proprioceptive feedback. Subjects actively scanned their right index finger over pairs of two-dimensional (2-D) angles (standard 90°; comparison 91–103°), identifying the larger one. Two exploratory strategies were tested: arm straight or arm flexed at the elbow so that joint movement was, respectively, mainly proximal (shoulder) or distal (wrist, finger). The mean discrimination thresholds for the sighted subjects (vision occluded) were similar for both exploratory strategies (5.7 and 5.8°, respectively). Exploratory strategy likewise did not modify threshold in the blind subjects (proximal 4.3°; distal 4.9°), but thresholds were on average lower than for the sighted subjects. A between-group comparison indicated that blind subjects had significantly lower thresholds than did the sighted subjects, but only for the proximal condition. The superior performance of the blind subjects likely represents heightened sensitivity to haptic inputs in response to visual deprivation, which, in these subjects, occurred prior to 14 years of age. <s> BIB004 </s> Tactual perception: a review of experimental variables and procedures <s> Blind participants <s> Abstract Previous studies have shown that blind subjects may outperform the sighted on certain tactile discrimination tasks. We recently showed that blind subjects outperformed the sighted in a haptic 2D-angle discrimination task. The purpose of this study was to compare the performance of the same blind (n = 16) and sighted (n = 17, G1) subjects in three tactile discrimination tasks dependent solely on cutaneous inputs from the fingertip of the index finger, D2. A second group of sighted subjects (n = 30, G2) were also tested. Texture discrimination thresholds were 0.62 (G1)–0.80 mm (G2) for the sighted subjects, and 0.64 mm for the blind (standard, 2 mm spatial period). Grating orientation thresholds were 0.99 (G1)–1.12 mm (G2) for the sighted subjects, and 0.96 mm for the blind. Finally, vibrotactile frequency discrimination thresholds (100 Hz standard) were 19.5 (G2) and 20.0 Hz (G1) for the sighted, and 16.5 Hz for the blind subjects. There were no significant differences in performance between the blind and the sighted subjects for the grating orientation or vibrotactile frequency discrimination tasks. In contrast, blind subjects outperformed the sighted for the texture discrimination task (G2 only), possibly reflecting the fact that the raised dot surfaces were similar to the dots forming Braille characters (all were fluent Braille readers). <s> BIB005 </s> Tactual perception: a review of experimental variables and procedures <s> Blind participants <s> We investigated and compared the acquisition of haptic concepts by the blind with the acquisition of haptic concepts by sighted controls. Each subject—blind, sighted but blindfolded, sighted and touching, and sighted only-initially classified eight objects into two categories using a study/test format, followed by a recognition/classification test involving old, new, and prototype forms. Each object varied along the dimensions of shape, size, and texture, with each dimension having five values. The categories were linearly separable in three dimensions, but no single dimension permitted 100% accurate classification. The results revealed that blind subjects learned the categories quickly and comparably with sighted controls. On the classification test, all groups performed equivalently, with the category prototype classified more accurately than the old or new stimuli. The blind subjects differed from the other subjects on the recognition test in two ways: They were least likely to false alarm to novel patterns that belonged to the category but most likely to false alarm to the category prototype, which they falsely called “old” 100% of the time. We discuss these results in terms of current views of categorization. <s> BIB006 </s> Tactual perception: a review of experimental variables and procedures <s> Blind participants <s> Sighted blindfolded individuals can successfully classify basic facial expressions of emotion (FEEs) by manually exploring simple 2-D raised-line drawings (Lederman et al 2008, IEEE Transactions on Haptics1 27–38). The effect of training on classification accuracy was assessed by sixty sighted blindfolded participants (experiment 1) and by three adventitiously blind participants (experiment 2). We further investigated whether the underlying learning process(es) constituted token-specific learning and/or generalization. A hybrid learning paradigm comprising pre/post and old/new test comparisons was used. For both participant groups, classification accuracy for old (ie trained) drawings markedly increased over study trials (mean improvement = 76%, and 88%, respectively). Additionally, RT decreased by a mean of 30% for the sighted, and 31% for the adventitiously blind. Learning was mostly token-specific, but some generalization was also observed for both groups. The sighted classified novel drawings of all s... <s> BIB007 </s> Tactual perception: a review of experimental variables and procedures <s> Blind participants <s> We investigated the role of visual experience and visual imagery in the processing of two-dimensional (2-D) tactile patterns. The performance of early-blind (EB), late-blind (LB), and blindfolded sighted (S) adults in the recognition of 2-D raised-line patterns was compared. We also examined whether recognition of 2-D tactile patterns depends on the type of memory strategy (eg spatial, visuo-spatial, verbal, and kinesthetic) used by EB, LB, and S participants to perform the task. Significant between-group differences in the recognition performance have not been found despite significant between-group differences in self-reported memory strategies. Recognition performance does not vary significantly with the strategy, but correlates positively with visuo-spatial imagery abilities in the S participants. These findings may be taken to suggest that the difficulties some blind people experience with tactile pictures are not due to difficulties in processing 2-D tactile patterns. <s> BIB008 </s> Tactual perception: a review of experimental variables and procedures <s> Blind participants <s> Tactile working memory was found to be more developed in completely blind (congenital and acquired) than in semi-sighted subjects, indicating that experience plays a crucial role in shaping working memory. A model of working memory, adapted from the classical model proposed by Baddeley and Hitch (1) and Baddeley (2), is presented where the connection strengths of a highly cross-modal network are altered through experience. <s> BIB009 </s> Tactual perception: a review of experimental variables and procedures <s> Blind participants <s> This research examined whether visual and haptic map learning yield functionally equivalent spatial images in working memory, as evidenced by similar encoding bias and updating performance. In 3 experiments, participants learned 4-point routes either by seeing or feeling the maps. At test, blindfolded participants made spatial judgments about the maps from imagined perspectives that were either aligned or misaligned with the maps as represented in working memory. Results from Experiments 1 and 2 revealed a highly similar pattern of latencies and errors between visual and haptic conditions. These findings extend the well-known alignment biases for visual map learning to haptic map learning, provide further evidence of haptic updating, and most important, show that learning from the 2 modalities yields very similar performance across all conditions. Experiment 3 found the same encoding biases and updating performance with blind individuals, demonstrating that functional equivalence cannot be due to visual recoding and is consistent with an amodal hypothesis of spatial images. <s> BIB010
Historically, the study of touch and blindness has roots in philosophy, medicine and psychology. The idea of enhanced tactile and auditory perception in blind subjects (e.g., Cattaneo and Vecchi 2011) and the notion of sensory substitution (e.g., Bach-y-Rita 1972) are common in the literature. However, research shows that information from different sensory modalities is not always easily interchangeable (e.g.,  . Authors have considered the study of haptic perception with blind participants as relevant because studies with sighted participants might be resulting in an underestimation of haptic abilities  , since there are reports of enhanced haptic sensitivity in the blind (e.g.,  . Research with blind participants has suggested that they have better performance in haptic tasks than sighted participants, for instance blind participants were faster in a task that required matching of geometrical shapes to its cut-offs , but this advantage is not always present. In a study considering the discrimination of texture, grating orientation and vibrotactile frequency, blind participants showed an advantage only for texture discrimination, revealing equivalent performance to sighted participants in the other two tasks BIB005 ). Many authors have emphasised the role of practice in performance for touch (e.g., BIB009 , and within this perspective, one must consider that blind participants have a larger experience in perceiving objects mainly by touch than sighted participants, and this familiarisation might be modulating the results, at least for experiments in which the stimuli are common or familiar stimuli. However, BIB007 have shown that with the presentation of highly unfamiliar and uncommon stimuli, blind and sighted participants show equivalent learning rates. In this study, the authors showed that it was possible to perceive emotional facial expressions through schematic raised line drawings. Another central conclusion of this study was that blind participants could be trained to detect emotional facial expressions. Also, in a study, comparing performance in haptic recognition of twodimensional patterns with early-blind, late-blind and sighted participants, it was described that the three groups had similar rates of performance, although participants were reporting different memory strategies when encoding the stimuli BIB008 . The comparison of blind and sighted participants in an angle discrimination task showed better performance of the blind participants' group BIB004 . Participants had to touch two-dimensional angles with one finger and evaluate which one was the largest. Blind participants consistently revealed lower thresholds for angle discrimination. In a later study BIB005 ), the authors aimed to generalise this finding to other discrimination tasks and reported that the blind participants' advantage was not task independent. In this study, there were no differences between the groups (composed by the same participants who collaborated in the earlier study) in haptic perception for a grating orientation task and for a vibrotactile frequency task. However, blind participants performed better in a discrimination of texture task, which the authors attributed to the possible similarity between the presented dotted textures and Braille characters. Blind participants have shown faster performance in shape correspondence task . In this study, in a speeded task in which participants were asked to match shapes to their negative in a board as fast as possible, the blind participants' group was faster, but not more accurate than the sighted participants' group. However, in a non-speeded task, no differences were revealed between the two groups. In a study on haptic concepts BIB006 ), four groups (blind participants, sighted blindfolded participants, sighted and touching participants and sighted only participants) were asked to perform classification and recognition tasks with a set of objects varying on texture, shape and size. Results revealed that all participants took approximately the same amount of time to learn the categories. However, blind participants differed from the other groups by presenting fewer false alarms to new patterns that belonged to the category, and revealing more false alarms to the category prototype, which was falsely recalled in all trials. BIB003 showed that tactile acuity decreased as a function of age at the same rhythm for sighted and blind participants, resulting in slower Braille reading in the blind participants' group. Equivalence from spatial processing in vision and touch has also been reported in research with blind participants. For instance, learning of maps through vision in sighted participants or through touch in blind participants showed similar results, suggesting that haptic information does not need to be translated into visual codes and had direct access to spatial processing BIB010 . BIB002 showed that blind children could benefit as much from haptic pictures as sighted children benefit of visual pictures in educational settings. Children either heard a description of a rare animal or haptically explored a picture of the animal, and results showed that children in the second condition were able to remember more information about the animals. Another interesting and large group of results reported the existence of visual imagery in blind participants, questioning the notion that imagery is visual in nature, and suggesting the existence of shared components between vision and haptics (e.g., BIB001 ; and for a review ). According to some authors, mental imagery has to be understood as a group of complex processes that generate representations, and not only as a perceptual trace. From this point of view, mental images do not need to be visual in nature and can be elicited by other sensory modalities (e.g.,  . The previously presented studies allow the clarification of some concepts and permit a better understanding of how the brain works and adjusts to sensory deprivation. Studies with blind subjects make it possible to conceive a scheme of the brain where perception is not dominated by vision, and in which other sensory modality processes can be explained without the need to hypothesise the conversion of information to visual codes, even when we are talking about mental images. Overall, some studies with blind participants have suggested advantages in haptic perception when compared to sighted participants (e.g.,  . Nonetheless, the role of experience and familiarity has to be considered in data interpretation and performance of blind and sighted subjects in conditions that are novel or highly familiar for both groups, as well as conditions that are highly familiar to both, seems to be largely equivalent.