Why the whole is more than the sum of its parts: salience-driven overestimation in aggregated tactile sensations

Experimental psychology often studies perception analytically, reducing its focus to minimal sensory units, such as thresholds or just noticeable differences in a single stimulus. Here, in contrast, we examine a synthetic aspect: how multiple inputs to a sensory system are aggregated into an overall percept. Participants in three experiments judged the total stimulus intensity for simultaneous electrical shocks to two digits. We tested whether the integration of component somatosensory stimuli into a total percept occurs automatically, or rather depends on the ability to consciously perceive discrepancy among components (Experiment 1), whether the discrepancy among these components influences sensitivity or/and perceptual bias in judging totals (Experiment 2), and whether the salience of each individual component stimulus affects perception of total intensity (Experiment 3). Perceptual aggregation of two simultaneous component events occurred both when participants could perceptually discriminate the two intensities, and also when they could not. Further, the actual discrepancy between the stimuli modulated both participants’ sensitivity and perceptual bias: increasing discrepancies produced a systematic and progressive overestimation of total intensity. The degree of this bias depended primarily on the salience of the stronger stimulus in the pair. Overall, our results suggest that important nonlinear mechanisms contribute to sensory aggregation. The mind aggregates component inputs into a coherent and synthetic perceptual experience in a salience-weighted fashion that is not based on simple summation of inputs

The Nature of Sensory Experience: the Case of Taste and Tasting

Recently, psychologists and neuroscientists have provided a great deal of evidence showing that perceptual experiences are mostly multimodal. As perceivers, we don’t usually recognize them as such. We think of the experiences we are having as either visual, or auditory or tactile, not realising that they often arise from the fusion of different sensory inputs. The experience of tasting something is one such case. What we call ‘taste’ is the result of the multisensory integration of touch taste and smell. These unified flavour experiences provide a challenge when trying to reconcile the underlying processing story with the conscious experience of subjects, but they also challenge assumptions about our access to our own experiences and whether how we conceive of those experiences plays any in role in accounting for their ultimate nature

Peripheral and central mechanisms in acid induced visceral pain hypersensitivity in the human oesophagus

PhDIntroduction: Gastro-oesophageal reflux disease (GORD) affects 40% of Western populations. Many symptoms persist despite the resolution of inflammation or acid exposure. In these patients, visceral pain hypersensitivity (VPH), modulated peripherally and centrally, is believed to be important. Study 1: Full thickness human oesophageal samples were collected from 10 patients undergoing oesophagectomy. Using immunohistochemistry, the samples were stained with PGP 9.5, synapthophysin, TRPV1, TRPV4 and ASIC3. Within healthy areas of the human oesophagus, immunoreactive nerve fibres and ganglia were identified in the sub-epithelium and myenteric plexus. Within the epithelium, nerve endings were absent; however, ASIC3 was reliably identified in epitheliocytes. Study 2: Oesophageal biopsy samples from 36 individuals were collected during upper GI endoscopy; erosive oesophagitis, non-erosive reflux disease and controls. Symptoms were profiled using symptom severity scores, adapted from a validated questionnaire. Oesophageal mucosal biopsies were taken 3-5 cm above the lower oesophageal sphincter. Specific features of oesophageal mucosal epithelial ASIC3 were identified by immunohistochemistry, which were associated positively with an increase in symptom severity. Study 3: Oesophageal VPH can be induced in healthy volunteers using an established model of acid infusion. In total, 85 retrospective infusions from 57 volunteers were studied, and VPH was present in 70%. The model was shown to be safe and reproducible, but reliability of the model for drug studies was only valid provided control measures were observed. Study 4: Pregabalin is a centrally acting calcium channel blocker currently used for somatic neuropathic pain and partial seizures. Using the model described in study 3, a prospective, double-blinded, cross-over, placebo-controlled study in 15 healthy volunteers was performed. After an initial screening visit, the volunteers were randomised to either pregabalin or placebo. Pregabalin prevented or attenuated VPH at 30 and 90 minutes after acid sensitisation. Conclusion: The evidence for central sensitisation was further consolidated with the pregabalin study and peripheral sensitisation by the ASIC3 study. The evidence is important in the detection of predominant mechanisms underlying the symptoms of patients with GORD for both cohort development and targeted treatment