Attention and relative novelty in human perceptual learning

Four experiments examined the role of attention in human perceptual learning. In Experiment 1, participants were preexposed to a pair of visual (checkerboard) stimuli AX and BX, with common elements X and unique features A and B. A same-different task was then used to assess discrimination of AX and BX and a pair of control stimuli, CY and DY. In addition, participants' eye movements were recorded to assess the role of attentional processes. The results showed that preexposure enhanced discrimination between AX and BX. Furthermore, participants showed greater attention to the preexposed unique features A and B than to the novel unique features C and D, as measured by the eye gaze monitor. Experiments 2 and 3 examined the prediction that perceptual learning is due to the relative familiarity of the common and unique stimulus features. Experiment 4 replicated the intermixed-blocked effect and showed that the way in which AX and BX are presented is also important for perceptual learning. The results generally support the idea that intermixed preexposure to AX and BX increases attention to the unique stimulus features A and B. Some aspects of the results are consistent with a relative novelty account, whereas others implicate a high-level attentional process that is not driven by stimulus novelty.     

Attention and perceptual priming in the perceptual identification task

Prior research indicates that manipulations of attention during encoding sometimes affect perceptual implicit memory. Two hypotheses were investigated. One proposes that manipulations of attention affect perceptual priming only to the extent that they disrupt stimulus identification. The other attributes reduced priming to the disruptive effects of distractor selection. The role of attention was investigated with a variant of the Stroop task in which participants either read words, identified their color, or did both. Identifying the color reduced priming even when the word was also overtly identified. This result held regardless of whether color and word were presented as a single object (Experiments 1 and 2) or as separate objects (Experiment 4). When participants read and identified a color, the overt order of the responses did not matter; both conditions reduced priming relative to reading alone (Experiment 3). The results provide evidence against the stimulus-identification account but are consistent with the distractor-selection hypothesis.     

Attention improves perceptual quality

Attention has been demonstrated to affect response speed, signal detection, and perceptual enhancement. We wished to determine whether exogenously cued attention had the additional effect of improving the veridicality of perceptual representations. We determined the accuracy and precision of orientation judgments for static and dynamic stimuli when they were, and when they were not, exogenously cued (luminance change). Valid exogenous cues led to more accurate responses that were also quicker. The attentional accuracy benefits were robust to stimulus degradation. Since our task displayed only one test stimulus at a time, response biases cannot account for our results. We concluded that exogenous cues can lead to percepts that are, on average, more similar to the external stimulus. Thus, exogenous cuing can improve perceptual quality.     

Imprinting and perceptual learning

Filial responses are first considered by reference to the initial stimulus situations. Findings on variability in responsiveness of chicks are reported and discussed. Facilitated responsiveness subsequent to visual stimulation is reported. The concept of critical period is examined in the light of other workers' and our own findings; it is concluded that imprinting ends as a result of its own action rather than through the effects of fear. Following responses are further considered by reference to the influences of early experiences and the act of following upon the occurrence and strength of subsequent responses. The degree of attachment to a moving object tends to be proportional to the amount of experience. Individual chicks were allowed to spend several hours following a box in a runway and their ability to discriminate between familiar and unfamiliar moving objects and static environments was studied. Strong evidence for imprintability to environment has been found. Imprinting phenomena are discussed in terms of perceptual learning.     

Attention enhances apparent perceptual organization

Perceptual organization and selective attention are two crucial processes that influence how we perceive visual information. The former structures complex visual inputs into coherent units, whereas the later selects relevant information. Attention and perceptual organization can modulate each other, affecting visual processing and performance in various tasks and conditions. Here, we tested whether attention can alter the way multiple elements appear to be perceptually organized. We manipulated covert spatial attention using a rapid serial visual presentation task, and measured perceptual organization of two multielements arrays organized by luminance similarity as rows or columns, at both the attended and unattended locations. We found that the apparent perceptual organization of the multielement arrays is intensified when attended and attenuated when unattended. We ruled out response bias as an alternative explanation. These findings reveal that attention enhances the appearance of perceptual organization, a midlevel vision process, altering the way we perceive our visual environment.     

Visual perceptual learning

Perceptual learning refers to the phenomenon that practice or training in perceptual tasks often substantially improves perceptual performance. Often exhibiting stimulus or task specificities, perceptual learning differs from learning in the cognitive or motor domains. Research on perceptual learning reveals important plasticity in adult perceptual systems, and as well as the limitations in the information processing of the human observer. In this article, we review the behavioral results, mechanisms, physiological basis, computational models, and applications of visual perceptual learning.     

Acetylcholine and olfactory perceptual learning

Olfactory perceptual learning is a relatively long-term, learned increase in perceptual acuity, and has been described in both humans and animals. Data from recent electrophysiological studies have indicated that olfactory perceptual learning may be correlated with changes in odorant receptive fields of neurons in the olfactory bulb and piriform cortex. These changes include enhanced representation of the molecular features of familiar odors by mitral cells in the olfactory bulb, and synthetic coding of multiple coincident odorant features into odor objects by cortical neurons. In this paper, data are reviewed that show the critical role of acetylcholine (Ach) in olfactory system function and plasticity, and cholinergic modulation of olfactory perceptual learning at both the behavioral and cortical level.     

Attention in learning

Learners exhibit many apparently irrational behaviors in their use of cues, sometimes learning to ignore relevant cues or to attend to irrelevant ones. A learning phenomenon called highlighting seems especially to demand explanation in terms of learned attention. Highlighting complements the classic phenomenon of conditioned blocking, which has been shown to involve learned inattention. Highlighting and blocking, along with a wide spectrum of other perplexing learning phenomena, can be accounted for by recent connectionist models in which both attentional shifting and associative learning are driven by the rational goal of rapid error reduction.     

Attention and probabilistic sequence learning

Limitations of using fixed sequences of events in studies of learning in the sequential reaction-time task led us to develop a probabilistic version of the task. When sequences occur probabilistically, transitions usually follow a sequence, but with some small probability, events occur out of sequence. This variation on the paradigm provides new evidence associated with manipulations of attentional load. Most notably, single-task learning leads to particularly high error rates on improbable transitions, suggesting anticipation of the sequence. Dual-task learning shows sensitivity to the sequence (by reaction-time differences to probable and improbable transitions), but without inflated errors on improbable transitions. Sensitivity to the sequence and anticipatory errors disappeared when participants transferred from single-task learning to dual-task conditions, suggesting that what is learned with single-task practice cannot be applied under conditions of limited attention. When learners transferred from dual- to single-task conditions, sensitivity of RT to the sequence increased but anticipation errors remained the same, suggesting that attentional load limits performance, but not learning. Qualitative differences in performance result from variations in attentional resources, which may reflect different learning processes. Received: 17 February 1997 / Accepted: 5 January 1998     

Procedural learning in perceptual categorization

In two experiments, observers learned two types of category structures: those in which perfect accuracy could be achieved via some explicit rule-based strategy and those in which perfect accuracy required integrating information from separate perceptual dimensions at some predecisional stage. At the end of training, some observers were required to switch their hands on the response keys, whereas the assignment of categories to response keys was switched for other observers. With the rule-based category structures, neither change in response instructions interfered with categorization accuracy. However, with the information-integration structures, switching response key assignments interfered with categorization performance, but switching hands did not. These results are consistent with the hypothesis that abstract category labels are learned in rule-based categorization, whereas response positions are learned in information-integration categorization. The association to response positions also supports the hypothesis of a procedural-learning-based component to information integration categorization.     

Unconsciously learning task-irrelevant perceptual sequences

We demonstrated unconscious learning of task-irrelevant perceptual regularities in a Serial Reaction Time (SRT) task in both visual and auditory domains. Participants were required to respond to different letters (‘F’ or ‘J’, experiment 1) or syllables (‘can’ or ‘you’, experiment 2) which occurred in random order. Unbeknownst to participants, the color (red, green, blue or yellow) of the two letters or the tone (1–4) of the syllables varied according to certain rules. Reaction times indicated that people indeed learnt both the color and tonal regularities indicating that task-irrelevant sequence structure can be learned perceptually. In a subsequent prediction test of knowledge of the color or tonal cues using subjective measures, we showed that people could acquire task irrelevant knowledge unconsciously.     

Late maturation of auditory perceptual learning

Adults can improve their performance on many perceptual tasks with training, but when does the response to training become mature? To investigate this question, we trained 11‐year‐olds, 14‐year‐olds and adults on a basic auditory task (temporal‐interval discrimination) using a multiple‐session training regimen known to be effective for adults. The adolescents all began with performance in the adult range. However, while all of the adults improved across sessions, none of the 11‐year‐olds and only half of the 14‐year‐olds did. The adolescents who failed to learn did so even though the 10‐session training regimen provided twice the number of sessions required by adults to reach asymptotic performance. Further, over the course of each session, the performance of the adults was stable but that of the adolescents, including those who learned, deteriorated. These results demonstrate that the processes that underlie perceptual learning can continue to develop well into adolescence.