Marcus R. Watson

Extremely selective attention: eye-tracking studies of the dynamic allocation of attention to stimulus features in categorization.

Humans have an extremely flexible ability to categorize regularities in their environment, in part because of attentional systems that allow them to focus on important perceptual information. In formal theories of categorization, attention is typically modeled with weights that selectively bias the processing of stimulus features. These theories make differing predictions about the degree of flexibility with which attention can be deployed in response to stimulus properties. Results from 2 eye-tracking studies show that humans can rapidly learn to differently allocate attention to members of different categories. These results provide the first unequivocal demonstration of stimulus-responsive attention in a categorization task. Furthermore, the authors found clear temporal patterns in the shifting of attention within trials that follow from the informativeness of particular stimulus features. These data provide new insights into the attention processes involved in categorization.

Looking versus seeing: Strategies alter eye movements during visual search

Visual search can be made more efficient by adopting a passive cognitive strategy (i.e., letting the target “pop” into mind) rather than by trying to actively guide attention. In the present study, we examined how this strategic benefit is linked to eye movements. Results show that participants using a passive strategy wait longer before beginning to move their eyes and make fewer saccades than do active participants. Moreover, the passive advantage stems from more efficient use of the information in a fixation, rather than from a wider attentional window. Individual difference analyses indicate that strategies also change the way eye movements are related to search success, with a rapid saccade rate predicting success among active participants, and fewer and larger amplitude saccades predicting success among passive participants. A change in mindset, therefore, alters how oculomotor behaviors are harnessed in the service of visual search.

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.

Synesthesia and learning: a critical review and novel theory

Learning and synesthesia are profoundly interconnected. On the one hand, the development of synesthesia is clearly influenced by learning. Synesthetic inducers – the stimuli that evoke these unusual experiences – often involve the perception of complex properties learned in early childhood, e.g., letters, musical notes, numbers, months of the year, and even swimming strokes. Further, recent research has shown that the associations individual synesthetes make with these learned inducers are not arbitrary, but are strongly influenced by the structure of the learned domain. For instance, the synesthetic colors of letters are partially determined by letter frequency and the relative positions of letters in the alphabet. On the other hand, there is also a small, but growing, body of literature which shows that synesthesia can influence or be helpful in learning. For instance, synesthetes appear to be able to use their unusual experiences as mnemonic devices and can even exploit them while learning novel abstract categories. Here we review these two directions of influence and argue that they are interconnected. We propose that synesthesia arises, at least in part, because of the cognitive demands of learning in childhood, and that it is used to aid perception and understanding of a variety of learned categories. Our thesis is that the structural similarities between synesthetic triggering stimuli and synesthetic experiences are the remnants, the fossilized traces, of past learning challenges for which synsethesia was helpful.

Grapheme-color synaesthesia benefits rule-based Category learning

Researchers have long suspected that grapheme-color synaesthesia is useful, but research on its utility has so far focused primarily on episodic memory and perceptual discrimination. Here we ask whether it can be harnessed during rule-based Category learning. Participants learned through trial and error to classify grapheme pairs that were organized into categories on the basis of their associated synaesthetic colors. The performance of synaesthetes was similar to non-synaesthetes viewing graphemes that were physically colored in the same way. Specifically, synaesthetes learned to categorize stimuli effectively, they were able to transfer this learning to novel stimuli, and they falsely recognized grapheme-pair foils, all like non-synaesthetes viewing colored graphemes. These findings demonstrate that synaesthesia can be exploited when learning the kind of material taught in many classroom settings.

Temporal characteristics of overt attentional behavior during category learning

Many theories of category learning incorporate mechanisms for selective attention, typically implemented as attention weights that change on a trial-by-trial basis. This is because there is relatively little data on within-trial changes in attention. We used eye tracking and mouse tracking as fine-grained measures of attention in three complex visual categorization tasks to investigate temporal patterns in overt attentional behavior within individual categorization decisions. In Experiments 1 and 2, we recorded participants’ eye movements while they performed three different categorization tasks. We extended previous research by demonstrating that not only are participants less likely to fixate irrelevant features, but also, when they do, these fixations are shorter than fixations to relevant features. We also found that participants’ fixation patterns show increasingly consistent temporal patterns. Participants were faster, although no more accurate, when their fixation sequences followed a consistent temporal structure. In Experiment 3, we replicated these findings in a task where participants used mouse movements to uncover features. Overall, we showed that there are important temporal regularities in information sampling during category learning that cannot be accounted for by existing models. These can be used to supplement extant models for richer predictions of how information is attended to during the buildup to a categorization decision.

Person perception informs understanding of cognition during visual search

Does person perception—the impressions we form from watching others—hold clues to the mental states of people engaged in cognitive tasks? We investigated this with a two-phase method: In Phase 1, participants searched on a computer screen (Experiment 1) or in an office (Experiment 2); in Phase 2, other participants rated the searchers’ video-recorded behavior. The results showed that blind raters are sensitive to individual differences in search proficiency and search strategy, as well as to environmental factors affecting search difficulty. Also, different behaviors were linked to search success in each setting: Eye movement frequency predicted successful search on a computer screen; head movement frequency predicted search success in an office. In both settings, an active search strategy and positive emotional expressions were linked to search success. These data indicate that person perception informs cognition beyond the scope of performance measures, offering the potential for new measurements of cognition that are both rich and unobtrusive.

The effect of pharmacological intervention on contrast sensitivity deficits in phenylketonuria

Patients with the autosomal recessive disorder phenylketonuria (PKU) have elevated phenylalanine levels that impede production of tyrosine, a precursor to dopamine. Lowered dopamine levels lead to a number of deficits, including lowered visual contrast sensitivity (Diamond & Herzberg, 1996; Gramer et al, 2013; Stemerdink et al, 1999). In the present study we measured contrast sensitivity and blood phenylalanine and tyrosine levels on multiple visits in 10 PKU patients, 5 of whom began a course of sapropterin dihydrochloride (Kuvan®), which reduces phenylalanine levels (in some patients). The expectation was that initial contrast sensitivity would correlate with phenylalanine and tyrosine levels, and that in patients who responded well to sapropterin dihydrochloride, reduced phenylalanine levels would correspond to increased contrast sensitivity. Contrast thresholds for each PKU patient and age-matched controls were determined using a four-alternative forced-choice grating discrimination task with an adaptive staircase (the Freiburg Visual Acuity Test, Bach, 1996; 2007) at five spatial frequencies, on multiple visits (1-4 per patient). On Visit 1, prior to sapropterin dihydrochloride treatment, contrast thresholds were an average of 67% higher in PKU patients than in their age-matched controls, but no correlation between performance and phenylalanine or tyrosine levels was detectable. During sapropterin dihydrochloride treatment, however, phenylalanine levels dropped by half, and contrast sensitivity deficits disappeared entirely. Practice also played a role in improvement: threshold elevations were 10% lower on Visit 2 among those patients who had not begun treatment. Control participants displayed a similar degree of improvement on their second visit. Results during treatment suggest that sapropterin hydrochloride may be effective in reducing both phenylalanine levels and corresponding perceptual deficits in PKU patients. The practice effect, however, raises the possibility that only some of the contrast sensitivity deficit in PKU patients is the result of dopamine-related impairments in the retina or visual cortex. Meeting abstract presented at VSS 2015.