Interleaving Effects in Blindfolded Perceptual Learning Across Various Sensory Modalities.

Fragmented pictures of an object, which appear meaningless when seen for the first time, can easily be identified after the presentation of an unfragmented version of the same picture. The neuronal mechanism for such a rapid perceptual learning phenomenon is largely unknown. Recently, induced gamma band responses (GBRs) have been discussed as a possible physiological correlate of activity in cell assemblies formed by learning. The present study was designed to investigate the modulation of induced GBRs in a perceptual learning task by using a 128-channel EEG montage. In the first sequence of the experiment, fragmented pictures from the Snodgrass and Vandervart inventory were presented. The fragmentation of the pictures was selected that subjects were unable to identify them. In the second experimental sequence - the perceptual learning sequence - half of the pictures were displayed in their unfragmented version. In the third sequence, all pictures were presented again in the fragmented version. Now, subjects had to rate whether or not they could identify the images. Results showed an increase in spectral gamma power at parietal electrode sites for identified pictures. In addition, neural activity in the gamma band was highly synchronized between posterior electrodes. For pictures not presented in their complete version, we found no such pattern in the third sequence. From our results, we concluded that induced GBRs might represent a signature of synchronized neural activity in a Hebbian cell assembly, activated by the fragmented picture after perceptual learning took place. No difference between identified and unidentified pictures was found in the visual evoked potential in the same time range and in the evoked GBR in the same frequency range as the induced response.

Declarative memory depends on the hippocampus and related medial temporal lobe and diencephalic structures. Declarative memory has usually been found to be available to conscious recollection. A recent study (Chun and Phelps, Nat Neurosci 1999;2:844-847) found that damage to the medial temporal lobe (including the hippocampus) impaired performance on a perceptual learning task, yet the learning was accomplished in the absence of memory for the stimuli. This finding raised the possibility that some hippocampus-dependent tasks may be inaccessible to awareness and may be performed without evoking conscious memory processes. Using the same task, we show that when damage is confined largely to the hippocampal formation, perceptual learning is intact. Thus, the available data suggest that damage limited to the hippocampal formation does not impair nonconscious (nondeclarative) memory. Further, the data do not contradict the idea that hippocampus dependent memory is accessible to conscious recollection. Finally, perceptual learning was impaired in patients, with extensive damage to the medial temporal lobe and with additional variable damage to lateral temporal cortex.

Numerous studies adopting Posner peripheral cueing paradigms have shown that exogenous attentional orientation (EAO) to a salient-but-irrelevant stimulus involves two opposing attentional processes: early attentional capture and late attentional suppression. Recent evidence has indicated that long-term perceptual learning can induce involuntary attentional capture by nonsalient shapes. However, it remains unclear whether a well-trained nonsalient shape could exhibit a biphasic pattern of EAO similar to that observed with physically salient stimuli, including both an early exogenous attentional shift and a late inhibition of return (IOR). Through both a perceptual learning task and a classic peripheral cueing task, the current study showed that a well-trained nonsalient shape cue could exhibit a biphasic pattern of EAO. When compared with an untrained shape, a well-trained nonsalient shape facilitated subsequent target detection at short cue-target onset asynchronies (CTOAs, 200-300ms) and deteriorated target detection at a relatively long CTOA (800ms), but not at 400- to 600-ms CTOAs. As a comparison, a detectability-matched onset cue or luminance contrast cue elicited a facilitatory effect at 200- to 300-ms CTOAs and an inhibitory effect starting from 400-ms CTOA. A control eye-tracking experiment suggested that the absence of IOR effects at 400- to 600-ms CTOAs in the trained cue task was not due to fewer eye movements during the task. Our results indicated that, as opposed to physically salient stimuli, a well-trained nonsalient shape induced delayed IOR after an evident exogenous shift of visual attention. The different patterns of EAO processes support the notion that prior experience (such as perceptual learning) plays a unique role in modulating our exogenous attention. Possible underlying mechanisms are proposed.

As we begin to acquire a new motor skill, we face the dual challenge of determining and refining the somatosensory goals of our movements and establishing the best motor commands to achieve our ends. The two typically proceed in parallel, and accordingly it is unclear how much of skill acquisition is a reflection of changes in sensory systems and how much reflects changes in the brain's motor areas. Here we have intentionally separated perceptual and motor learning in time so that we can assess functional changes to human sensory and motor networks as a result of perceptual learning. Our subjects underwent fMRI scans of the resting brain before and after a somatosensory discrimination task. We identified changes in functional connectivity that were due to the effects of perceptual learning on movement. For this purpose, we used a neural model of the transmission of sensory signals from perceptual decision making through to motor action. We used this model in combination with a partial correlation technique to parcel out those changes in connectivity observed in motor systems that could be attributed to activity in sensory brain regions. We found that, after removing effects that are linearly correlated with somatosensory activity, perceptual learning results in changes to frontal motor areas that are related to the effects of this training on motor behavior and learning. This suggests that perceptual learning produces changes to frontal motor areas of the brain and may thus contribute directly to motor learning.

Electronic retinal prostheses, the only sight restoration technology currently approved for implantation in patients, cause simultaneous, rather than complementary firing within on- and off-center retinal cells. Here, using ‘virtual patients’ - sighted individuals viewing distorted input - we examine whether plasticity might compensate for the resulting neuronal population coding distortions. Four participants were trained in a perceptual learning task using dichoptic presentation of original and contrast-reversed images as a proxy for inappropriate on and off-cell stimulation. Each greyscale image (I) and its contrast-reverse (I′) was filtered using a radial checkerboard in Fourier space (F) and its inverse (F'). [I * F?] + [I′* F] was presented to one eye, [I * F] + [I' * F?] to the other, such that regions producing on-responses in one eye produce off-responses in the other eye.

Human performance in visual detection, discrimination, identification, and search tasks typically improves with practice. Psychophysical studies suggest that perceptual learning is mediated by an enhancement in the coding of the signal, and physiological studies suggest that it might be related to the plasticity in the weighting or selection of sensory units coding task relevant information (learning through attention optimization). We propose an experimental paradigm (optimal perceptual learning paradigm) to systematically study the dynamics of perceptual learning in humans by allowing comparisons to that of an optimal Bayesian algorithm and a number of suboptimal learning models. We measured improvement in human localization (eight-alternative forced-choice with feedback) performance of a target randomly sampled from four elongated Gaussian targets with different orientations and polarities and kept as a target for a block of four trials. The results suggest that the human perceptual learning can occur within a lapse of four trials (<1 min) but that human learning is slower and incomplete with respect to the optimal algorithm (23.3% reduction in human efficiency from the 1st-to-4th learning trials). The greatest improvement in human performance, occurring from the 1st-to-2nd learning trial, was also present in the optimal observer, and, thus reflects a property inherent to the visual task and not a property particular to the human perceptual learning mechanism. One notable source of human inefficiency is that, unlike the ideal observer, human learning relies more heavily on previous decisions than on the provided feedback, resulting in no human learning on trials following a previous incorrect localization decision. Finally, the proposed theory and paradigm provide a flexible framework for future studies to evaluate the optimality of human learning of other visual cues and/or sensory modalities.

Although the majority of research on human memory has concentrated on a person's ability to recall or recognize items as having been presented in a particular situation, the effects of memory are also revealed in a person's performance of a perceptual task. Prior experience with material can make that material more easily identified or comprehended in perceptually difficult situations. Unlike with standard retention tests, effects of prior experience on a perceptual task do not logically require that a person be aware that he or she is remembering. Indeed, amnesic patients purportedly show effects of practice in their subsequent performance of a perceptual or motor task even though they profess that they do not remember having engaged in that prior experience. The experiments that are reported were designed to explore the relationship between the more aware autobiographical form of memory that is measured by a recognition memory test and the less aware form of memory that is expressed in perceptual learning. Comparisons of effects on perceptual learning and recognition memory reveal two classes of variables. Variables such as the level of processing of words during study influenced recognition memory, although they had no effect on subsequent perceptual recognition. A study presentation of a word had as large an effect on its later perceptual recognition when recognition memory performance was very poor as it did when recognition memory performance was near perfect. In contrast, variables such as the number and the spacing of repetitions produced parallel effects on perceptual recognition and recognition memory. Following Mandler and others, it is suggested that there are two bases for recognition memory. If an item is readily perceived so that it seems to "jump out" from the page, a person is likely to judge that he or she has previously seen the item in the experimental situation. Variables that influence ease of perceptual recognition, then, can also have an effect on recognition memory, so parallel effects are found. The second basis for recognition memory involves elaboration of a word's study context and depends on such factors as level of processing during study--factors that are not important for perceptual recognition of isolated words. Comparisons of perceptual recognition and recognition memory are shown to be useful for determining how a variable has its effect. Effects of study on perceptual recognition appear to be totally due to memory for physical or graphemic information. Results reported are also relevant to theories of perceptual learning. A single presentation of an item is shown to have large and long-lasting effects on its later perceptual recognition. At least partially, effects of study on perceptual recognition depend on the same variables as do effects on more standard memory tests.

The purpose of this study was to evaluate the integrative effects of visual stimuli with chemical senses (olfactory and gustatory) stimuli in humans. Noninvasive measurement tools such as magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI) are used to describe the mechanism of olfactory information processing in the human brain, and the neurophysiological properties of olfactory-related neurons are described. The first study analyzed the interaction between visual and olfactory stimuli. Two odors (lemon and iso-valeric acid) were selected as pleasant and unpleasant odors, respectively and pleasant and unpleasant images were also selected. These cross-modal stimulus combinations were presented to the subject at random, and responses were measured by fMRI using an event related task. These results revealed that active brain areas with pleasant/unpleasant stimuli and matched/mismatched stimuli were different for memory and cognition. The second study analyzed the interaction between visual and gustatory stimuli. Total four conditions (hunger-not hunger, and intake-not intake of monosodium glutamate (MSG)) were tested. Visual stimuli were food-related and nonfood-related photos. A visual analog scale (VAS) was also used to evaluate before and at regular time intervals after intake of MSG, and responses were measured using fMRI. Brain activity related to feeding desire after intake of MSG occurred near the insula cortex, and orbito-frontal cortex, among other areas. These results on the integrative effects of visual stimuli with olfactory and gustatory stimuli, cross-modal and complex effects on olfaction and gustation were suggested to be obtained as an emotional response such as "pleasantness/unpleasantness" and as cognitive and memory responses such as "matching/mismatching" or the responses such as "feeding desire" afterwards intake of foods.

Thirty-six participants were tested on inattentional blindness (IB), inattentional insensitivity for tactile stimuli, and inattentional insensitivity for olfactory stimuli. Inattentional insensitivity (IIS) is the inability to detect the sensation of a salient stimulus while performing a task within a congruent sensory modality. The Invisible Gorilla video (Simons, 2003) was used to test IB. Half of the participants were tasked while engaged in each sensory condition, and half of the participants were not tasked. Chi square analyses showed that tasked participants displayed more IB than nontasked participants. In addition, tasked participants in the tactile condition displayed more IIS for a salient tactile stimulus than participants who were not tasked. No differences were found between groups for IIS in the olfactory condition. High working memory (WM) participants showed better performance than low WM participants in the tactile task. High WM participants also showed better performance during the visual condition (i.e., higher accuracy for basketball counts). Finally, results suggest a possible relationship between IIS with performance across different sensory modalities.

Visual category learning (VCL) involves detecting which features are most relevant for categorization. VCL relies on attentional learning, which enables effectively redirecting attention to object’s features most relevant for categorization, while ‘filtering out’ irrelevant features. When features relevant for categorization are not salient, VCL relies also on perceptual learning, which enables becoming more sensitive to subtle yet important differences between objects. Little is known about how attentional learning and perceptual learning interact when VCL relies on both processes at the same time. Here we tested this interaction. Participants performed VCL tasks in which they learned to categorize novel stimuli by detecting the feature dimension relevant for categorization. Tasks varied both in feature saliency (low-saliency tasks that required perceptual learning vs. high-saliency tasks), and in feedback information (tasks with mid-information, moderately ambiguous feedback that increased attentional load, vs. tasks with high-information non-ambiguous feedback). We found that mid-information and high-information feedback were similarly effective for VCL in high-saliency tasks. This suggests that an increased attentional load, associated with the processing of moderately ambiguous feedback, has little effect on VCL when features are salient. In low-saliency tasks, VCL relied on slower perceptual learning; but when the feedback was highly informative participants were able to ultimately attain the same performance as during the high-saliency VCL tasks. However, VCL was significantly compromised in the low-saliency mid-information feedback task. We suggest that such low-saliency mid-information learning scenarios are characterized by a ‘cognitive loop paradox’ where two interdependent learning processes have to take place simultaneously.

This study examined whether older adults remain perceptually flexible when presented with ambiguities in speech in the absence of lexically disambiguating information. We expected older adults to show less perceptual learning when top-down information was not available. We also investigated whether individual differences in executive function predicted perceptual learning in older and younger adults. Younger (n = 31) and older adults (n = 27) completed 2 perceptual learning tasks composed of a pretest, exposure, and posttest phase. Both learning tasks exposed participants to clear and ambiguous speech tokens, but crucially, the lexically guided learning task provided disambiguating lexical information whereas the distributional learning task did not. Participants also performed several cognitive tasks to investigate individual differences in working memory, vocabulary, and attention-switching control. We found that perceptual learning is maintained in older adults, but that learning may be stronger in contexts where top-down information is available. Receptive vocabulary scores predicted learning across both age groups and in both learning tasks. Implicit learning is maintained with age across different learning conditions but remains stronger when lexically biasing information is available. We find that receptive vocabulary is relevant for learning in both types of learning tasks, suggesting the importance of vocabulary knowledge for adapting to ambiguities in speech.

Perceptual learning (PL) involves long-lasting improvement in perceptual tasks following extensive training and is accompanied by modified neuronal responses in sensory cortical areas in the brain. Understanding the dynamics of PL and the resultant synaptic changes is important for causally connecting PL to the observed neural plasticity. This is theoretically challenging because learning-related changes are distributed across many stages of the sensory hierarchy. In this paper, we modeled the sensory hierarchy as a deep nonlinear neural network and studied PL of fine discrimination, a common and well-studied paradigm of PL. Using tools from statistical physics, we developed a mean-field theory of the network in the limit of a large number of neurons and large number of examples. Our theory suggests that, in this thermodynamic limit, the input-output function of the network can be exactly mapped to that of a deep linear network, allowing us to characterize the space of solutions for the task. Surprisingly, we found that modifying synaptic weights in the first layer of the hierarchy is both sufficient and necessary for PL. To address the degeneracy of the space of solutions, we postulate that PL dynamics are constrained by a normative minimum perturbation (MP) principle, which favors weight matrices with minimal changes relative to their prelearning values. Interestingly, MP plasticity induces changes to weights and neural representations in all layers of the network, except for the readout weight vector. While weight changes in higher layers are not necessary for learning, they help reduce overall perturbation to the network. In addition, such plasticity can be learned simply through slow learning. We further elucidate the properties of MP changes and compare them against experimental findings. Overall, our statistical mechanics theory of PL provides mechanistic and normative understanding of several important empirical findings of PL.

Neural correlates of responses to emotionally valenced olfactory, visual, and auditory stimuli were examined using positron emission tomography. Twelve volunteers were scanned using the water bolus method. For each sensory modality, regional cerebral blood flow (rCBF) during presentation of both pleasant and unpleasant stimuli was compared with that measured during presentation of neutral stimuli. During the emotionally valenced conditions, subjects performed forced-choice pleasant and unpleasant judgments. During the neutral conditions, subjects were asked to select at random one of a two key-press buttons. All stimulations were synchronized with inspiration, using an airflow olfactometer, to present the same number of stimuli for each sensory modality. A no-stimulation control condition was also performed in which no stimulus was presented. For all three sensory modalities, emotionally valenced stimuli led to increased rCBF in the orbitofrontal cortex, the temporal pole, and the superior frontal gyrus, in the left hemisphere. Emotionally valenced olfactory and visual but not auditory stimuli produced additional rCBF increases in the hypothalamus and the subcallosal gyrus. Only emotionally valenced olfactory stimuli induced bilateral rCBF increases in the amygdala. These findings suggest that pleasant and unpleasant emotional judgments recruit the same core network in the left hemisphere, regardless of the sensory modality. This core network is activated in addition to a number of circuits that are specific to individual sensory modalities. Finally, the data suggest a superior potency of emotionally valenced olfactory over visual and auditory stimuli in activating the amygdala.

Two experiments were conducted that examined information integration and rule-based category learning, using stimuli that contained auditory and visual information. The results suggest that it is easier to perceptually integrate information within these sensory modalities than across modalities. Conversely, it is easier to perform a disjunctive rule-based task when information comes from different sensory modalities, rather than from the same modality. Quantitative model-based analyses suggested that the information integration deficit for across-modality stimulus dimensions was due to an increase in the use of hypothesis-testing strategies to solve the task and to an increase in random responding. The modeling also suggested that the across-modality advantage for disjunctive, rule-based category learning was due to a greater reliance on disjunctive hypothesis-testing strategies, as opposed to unidimensional hypothesis-testing strategies and random responding.

Reproductive status influences multisensory integration responses in female round gobies, Neogobius melanostomus