An n-back task using vibrotactile stimulation with comparison to an auditory analogue

We report a vibrotactile version of the common n-back task used to study working memory. Subjects wore vibrotactile stimulators on three fingers of one hand, and they responded by pressing a button with the other hand whenever the current finger matched the one stimulated n items back. Experiment 1 showed a steep decline in performance as n increased from 1 to 3; each additional level ofn decreased performance by 1.5 d' units on average. Experiment 2 supported a central capacity locus for the vibrotactile task by showing that it correlated strongly with an auditory analogue; both tasks were also related to standard digit span. The vibrotactile version of n-back may be particularly useful in dual-task contexts. It allows the assessment of cognitive capacity in sensory-impaired populations in which touch remains intact, and it may find use in brain-imaging studies in which vibrotactile stimuli impose a memory load.     

Performance in a delayed comparison discrimination task as a function of stimulus interpretation

In a sequential same-different comparison task, physically similar visual stimuli with the same interpretation were more poorly discriminated than equally similar stimuli with different interpretations. Physical similarity of stimulus pairs was held constant by using parametrically controlled computer-generated visual forms and by using each pair of figures as both a sameinterpretation pair and as a different-interpretation pair. The interpretation variable used the ambiguous-figure properties of the forms. The two forms in each pair could be seen as representing the same object given one way of interpreting them; a second interpretation applied to only one member of the pair. The discrimination results held for interstimulus intervals of 300 msec and 13 sec. Similarities between the present studies and “categorical perception” studies are noted.     

The initial effect of noise on a simple vibrotactile learning task

In two experiments the effect of loud noise on a simple vibrotactile learning task was studied. After learning the task to criterion, 10 male and 10 female Ss received two pairs of test trials, one without noise, and one in continuous noise (a 1,000 cps pure tone at 90 dB SPL). An additional 10 male and 10 female Ss learned the same task and also received the same two pairs of test trials, but instead of receiving continuous noise for the second condition, they received an intermittent noise (random numbers presented at 2 sec intervals at 95 dB SPL). In the first experiment noise had a significant effect on the performance of the 20-subject group and also on the females in the group. Noise did not significantly affect the performance of males. In the second experiment noise had no significant effect on either males or females.     

Learning conditional frequencies in a probability learning task

The study was prompted by a theoretical discussion of probability learning by Estes (1976). In three separate experiments, subjects were presented with frequency information in the form of wins and losses among 3 teams, and later predicted future wins and losses. Frequencies were devised so that conditional win frequencies for a pair of teams were either inconsistent or consistent with marginal win frequencies for each team. In experiment 1, when subjects predicted future events on the basis of known past frequencies, predictions were generally based on conditional frequencies. In experiment 2 six blocks of observations were presented, with predictions following each block. What little learning did occur was in the direction of the conditional frequencies. Subjects in experiment 3 were able to learn conditional frequencies when given explicit instructions to do so. Results were discussed in terms of a two-stage hypothesis generation model that might operate within the framework of an associative theory of probability learning.     

Reinforcer efficacy in a delayed matching-to-sample task.

Five domestic hens were exposed to a delayed matching-to-sample task. Conditions 1, 5, and 8 were variable-delay conditions in which five delays (0.25, 1, 2, 4, and 8 s) from the red or green sample to the presentation of the red and green comparison stimuli were presented a number of times during each session. In the fixed-delay condition (Condition 3), each delay was presented for 15 sessions under a Latin square design across birds. When improvements in accuracy across the variable-delay conditions are taken into account, the data were similar under both the variable and fixed delays. In Conditions 2, 4, 6, and 7 sample-reinforcer intervals were held at 8, 8, 4, and 2 s, respectively, while sample-choice intervals were varied within these during each session. With increasing sample-reinforcer interval, both initial discriminability (i.e., with sample-choice delay = 0) and rate of decrement in discriminability decreased. Although the former would be predicted if accuracy depends of the average sample-reinforcer interval, the latter would not. These data show that increasing the sample-choice interval had less effect on matching accuracy than increasing the sample-reinforcer interval did.     

Unitary classification in a comparison task

Sequential effects were used to diagnose whether elements in a two-object-comparison-task are represented as a perceptual unit or separately. The presence of sequential effects and absence of influences of individual elements on the subsequent trial in a successive comparison task favor the hypothesis that the elements in a pair are represented as a unit, and that a response is made to the perceptual unit. The patterns of responsetimes onsame anddifferent trials differed in-several ways; these suggested that the quality of the representations ofsame anddifferent trials may differ.     

Verbal interference in a perceptual comparison task

When Ss had to indicate if the colors of pairs of items from the Stroop test were the same or different, the usual interference effect was completely eliminated. However, when the verbal information consisted of SAME and DIFF rather than color names, interference was reestablished. This indicates that the perceptual comparison task does not eliminate interference simply by rendering Ss insensitive to the meanings of words.     

Anisomycin impairs long-term working memory in a delayed alternation task

A long-term temporal component of working memory of rats trained on the radial maze has been shown to be susceptible to disruption by the protein synthesis inhibitor, anisomycin. It is not clear whether protein synthesis played a role in working memory because accurate performance on the radial maze required the storage of a large amount of information, or because the information was to be held in store for relatively long periods of time. This experiment tested these hypotheses by assessing the effect of anisomycin on choice accuracy in a comparatively simple spatial delayed alternation task. Results indicate that under the present training conditions, protein involvement in working memory is related more to the length of the retention interval than to the amount of information retained.     

Unitary classification in a comparison task.

Sequential effects were used to diagnose whether elements in a two-object comparison task are represented as a perceptual unit or separately. The presence of sequential effects and absence of influences of individual elements on the subsequent trial in a successive comparison task favor the hypothesis that the elements in a pair are represented as a unit, and that a response is made to the perceptual unit. The patterns of response times on same and different trials differed in several ways; these suggested that the quality of the representations of same and different trials may differ.     

A comparison of discrimination and identification of vibrotactile patterns

Both discrimination and identification tasks have been used to assess subjects' abilities to perceive vibratory spatial patterns presented to the skin. The present study examined discrimination and identification performance under comparable conditions. In Experiment 1, subjects attempted to discriminate a pair of patterns on some blocks of trials and to identify both members of a pair on other blocks. For both tasks, the time between the members of the pair was varied. Discrimination performance could be predicted accurately from identification data. Analysis of performance on identification trials indicated that subjects used discriminability information to identify pairs. In Experiment 2, discrimination and identification were compared when the temporal separation between patterns was fixed and a masking stimulus followed each pattern after a variable delay. Results suggest that temporal masking, rather than the time available for processing pattern information, is the major limitation in both discrimination and identification of sequences of tactile patterns.     

Neural correlates of a default response in a delayed go/no-go task

Working memory, the ability to temporarily retain task-relevant information across a delay, is frequently investigated using delayed matching-to-sample (DMTS) or delayed Go/No-Go tasks (DGNG). In DMTS tasks, sample cues instruct the animal which type of response has to be executed at the end of a delay. Typically, performance decreases with increasing delay duration, indicating that working memory fades across a delay. However, no such performance decrease has been found when the sample cues exist of present vs. absent stimuli, suggesting that pigeons do not rely on working memory, but seem to respond by default in those trials. We trained 3 pigeons in a DGNG task and found a similar default response pattern: The diverging slopes of the retention functions on correct Go and No-Go trials suggested that pigeons by default omitted their response following No-Go stimuli, but actively retained task-relevant information across the delay for successful responses on Go trials. We conducted single-cell recordings in the avian nidopallium caudolaterale, a structure comparable to the mammalian prefrontal cortex. On Go trials, many neurons displayed sustained elevated activity during the delay preceding the response, replicating previous findings and suggesting that task-relevant information was neurally represented and maintained across the delay. However, the same units did not show enhanced delay activity preceding correct response suppressions in No-Go trials. This activation-inactivation pattern presumably constitutes a neural correlate of the default response strategy observed in the DGNG task.     

Short-term visual memory for contour curvature in a delayed discrimination task

Abstract: A two-interval forced-choice of constant stimuli was used to measure the point of subjective equality (PSE) and discrimination threshold for standard contour curvature (1.91, 3.24 deg⁻¹) held in short-term visual memory (STVM). At both standard curvatures, the PSE for remembered curvature was nearly constant for standard curvature from 2 s to 16 s retention intervals, while the discrimination threshold increased as a linear function of retention interval. These results show that the decay in STVM for contour curvature is due to the noisy representation of curvature, neither to fading of the represented curvature nor to converging to the constant curvature. Furthermore, the Weber fraction was nearly constant for both standard curvatures at any delay from 2 to 16 s.     

Semantic association effects in a mental comparison task

Two reaction time experiments explored the effect of semantic associations on the time required to make mental size comparisons. Subjects in both experiments were able to judge relative size more quickly for associated than for nonassociated pairs. This association effect was found for a variety of different types of semantic relationships. Experiment 2 used a large pool of pairs that were scaled for degree of association and subjective size of the individual items. This experiment demonstrated that a high degree of association is more facilitative for pairs with small rather than large size differences. Two different explanations of the results are presented, and it is tentatively suggested that work on mental comparison may be integrated with a broader range of semantic memory research.     

Numeric comparison in a visually-guided manual reaching task

Nearly all studies on perception and cognition have used discrete responses to infer internal cognitive processes. In the current study, we demonstrate that visually-guided manual reaching can provide new opportunities to access internal processes over time. In each trial, participants were required to compare a single digit Arabic number presented on the center square with the standard, 5. Participants were asked to reach and touch one of three squares on the screen with their index finger while their hand movement trajectories were recorded: the left square for 1-4, the center for 5, and the right for 6-9. Direct evidence for an analogue representation of numbers was found in early as well as in later portions of hand trajectories, showing systematic shifts in position for small differences in numerical magnitude.     

Evidence of precurrent responses expanding equivalence classes in a delayed matching-to-sample task

Delayed matching to sample (DMTS) increases the probability of equivalence class formation. Precurrent responses can mediate the retention interval in DMTS trials and control the selection of comparisons. In human participants, precurrent responses usually consist of naming the experimental stimuli based on their similarities to meaningful stimuli with preexperimental history. We tested whether precurrents expand classes by serving as nodes between experimental and meaningful stimuli. A DMTS (2 s) was used throughout the entire experiment. Eleven undergraduates learned A1B1 and A2B2 relations and then were submitted to ArC trials that required them to answer math problems presented during the DMTS interval: when the sample was A1, the problems resulted in 12 and C1 was correct; when the sample was A2, they resulted in 9 and C2 was correct. Response-as-node tests assessed whether participants would relate B1 and C1 to the printed number 12 and B2 and C2 to the printed number 9. Ten participants responded accordingly to this pattern, showing that the responses to the problems expanded the classes. Parity tests using the words “even” and “odd” further confirmed this hypothesis. These results contribute to understanding why DMTS enhances equivalence performances. Implications of using this procedure in stimulus-equivalence studies are discussed.     

Spontaneous private speech and performance on a delayed match-to-sample task

Spontaneous private speech samples were obtained from 65 kindergarten children (mean age 70.3 months) from one suburban (n = 36) and one city (n = 29) school as they worked alone on a delayed match-to-sample (DMS) task with three levels of difficulty (2, 10, and 30 sec delays). As expected increases in DMS delay intervals produced decreased performance and increases in private speech. The expected increased positive relationship between task relevant private speech and performance for longer delays was found in city children but not suburban children. Since mean IQ scores were significantly different for the two groups this variable was further examined in post hoc analyses and discussed along with socio-economic status as possible explanations for the observed school-sample differences. A within-subject comparison for all children showed the percentage of speaking trials correct at 30-sec delay to be significantly greater than the percentage of nonspeaking trials correct. The effect of one experimenter modeled trial on a subsequent 10 trials at 30-sec delay was to increase speech and performance and to show a stronger relationship between speech and performance than for premodeling trials. These exploratory findings with a relatively simple two color matching task suggest further explorations of spontaneous private speech as a way of studying internalization of self regulatory cognitive strategies.     

Modality-specific interference with overt mediation by pigeons in a delayed discrimination task

Pigeons were trained on a delayed discrimination task in which they were rewarded for pecking a white terminal stimulus (TS) presented 5 sec after a green initial stimulus (IS) and for not pecking the white TS when it followed a red IS. Each bird bridged the memory interval (MI) with overt mediational behaviors. Nevertheless, sustained retroactive interference (RI) effects were produced by houselight illumination (Experiments 1 and 3), and mild shock pulses (Experiment 5) but not white noise (Experiment 2) presented during the MI. Although the magnitude of the light-induced RI effect was proportional to the duration of houselight illumination (Experiment 4), the beginning-end effect described by W. A. Roberts and D. S. Grant (Journal of Experimental Psychology: Animal Behavior Processes, 1978, 4, 219–236) was not observed. These results not only attest to the between-task robustness of both light-induced RI and modality-specific effects with pigeons, but also support the hypothesis that RI effects result from the disruption of mediational activities possibly analogous to rehearsal. The results further demonstrate that an event interpolated within the MI need not be unexpected or novel to produce RI. Furthermore, the interpolated event can produce modality-specific RI effects even though it effects a different sense than do the IS and TS.     

Reinforcer control by comparison-stimulus color and location in a delayed matching-to-sample task

Six pigeons were trained in a delayed matching-to-sample task involving bright- and dim-yellow samples on a central key, a five-peck response requirement to either sample, a constant 1.5-s delay, and the presentation of comparison stimuli composed of red on the left key and green on the right key or vice versa. Green-key responses were occasionally reinforced following the dimmer-yellow sample, and red-key responses were occasionally reinforced following the brighter-yellow sample. Reinforcer delivery was controlled such that the distribution of reinforcers across both comparison-stimulus color and comparison-stimulus location could be varied systematically and independently across conditions. Matching accuracy was high throughout. The ratio of left to right side-key responses increased as the ratio of left to right reinforcers increased, the ratio of red to green responses increased as the ratio of red to green reinforcers increased, and there was no interaction between these variables. However, side-key biases were more sensitive to the distribution of reinforcers across key location than were comparison-color biases to the distribution of reinforcers across key color. An extension of Davison and Tustin's (1978) model of DMTS performance fit the data well, but the results were also consistent with an alternative theory of conditional discrimination performance (Jones, 2003) that calls for a conceptually distinct quantitative model.     

Measuring perceived ceiling height in a visual comparison task

When judging interior space, a dark ceiling is judged to be lower than a light ceiling. The method of metric judgments (e.g., on a centimetre scale) that has typically been used in such tasks may reflect a genuine perceptual effect or it may reflect a cognitively mediated impression. We employed a height-matching method in which perceived ceiling height had to be matched with an adjustable pillar, thus obtaining psychometric functions that allowed for an estimation of the point of subjective equality (PSE) and the difference limen (DL). The height-matching method developed in this paper allows for a direct visual match and does not require metric judgment. It has the added advantage of providing superior precision. Experiment 1 used ceiling heights between 2.90?m and 3.00?m. The PSE proved sensitive to slight changes in perceived ceiling height. The DL was about 3% of the physical ceiling height. Experiment 2 found similar results for lower (2.30?m to 2.50?m) and higher (3.30?m to 3.50?m) ceilings. In Experiment 3, we additionally varied ceiling lightness (light grey vs. dark grey). The height matches showed that the light ceiling appeared significantly higher than the darker ceiling. We therefore attribute the influence of ceiling lightness on perceived ceiling height to a direct perceptual rather than a cognitive effect.