No position-specific interference from prior lists in cued recognition: A challenge for position coding (and other) theories of serial memory.

Position-specific intrusions of items from prior lists are rare but important phenomena that distinguish broad classes of theory in serial memory. They are uniquely predicted by position coding theories, which assume items on all lists are associated with the same set of codes representing their positions. Activating a position code activates items associated with it in current and prior lists in proportion to their distance from the activated position. Thus, prior list intrusions are most likely to come from the coded position. Alternative "item dependent" theories based on associations between items and contexts built from items have difficulty accounting for the position specificity of prior list intrusions. We tested the position coding account with a position-cued recognition task designed to produce prior list interference. Cuing a position should activate a position code, which should activate items in nearby positions in the current and prior lists. We presented lures from the prior list to test for position-specific activation in response time and error rate; lures from nearby positions should interfere more. We found no evidence for such interference in 10 experiments, falsifying the position coding prediction. We ran two serial recall experiments with the same materials and found position-specific prior list intrusions. These results challenge all theories of serial memory: Position coding theories can explain the prior list intrusions in serial recall and but not the absence of prior list interference in cued recognition. Item dependent theories can explain the absence of prior list interference in cued recognition but cannot explain the occurrence of prior list intrusions in serial recall.

Serial attention to serial memory: The psychological refractory period in forward and backward cued recall.

Guided by the conjecture that memory retrieval is attention turned inward, we examined serial attention in serial memory, combining the psychological refractory period (PRP) procedure from attention research with cued recall of two items from brief six-item lists. We report six experiments showing robust PRP effects in cued recall from memory (1-4) and cued report from perceptual displays (5-6), which suggest that memory retrieval requires the same attentional bottleneck as "retrieval" from perception. There were strong direction effects in each memory experiment. Response time (RT) was shorter and accuracy was higher when the cues occurred in the forward direction (left-to-right, top-to-bottom, first-to-last), replicating differences between forward and backward serial recall. Cue positions had strong effects on RT and accuracy in the memory experiments (1-4). The pattern suggested that subjects find cued items in memory by stepping through the list from the beginning or the end, with a preference for starting at the beginning. The perceptual experiments (5-6) showed weak effects of position that were more consistent with direct access. In all experiments, the distance between the cues in the list (lag) had weak effects, suggesting that subjects searched for each cue from the beginning or end of the list more often than they moved through the list from the first cue to the second. Direction, distance, and lag effects on RT and inter-response interval changed with SOA in a manner that suggested they affect bottleneck or pre-bottleneck processes that create and execute a plan for successive retrievals. We conclude that sequential retrieval from memory and sequential attention to perception engage the same computations and we show how computational models of memory can be interpreted as models of attention focused on memory.

The spotlight turned inward: the time-course of focusing attention on memory.

Guided by the idea that memory retrieval is selective attention turned inward, we report four experiments examining the time-course of focusing attention on memory. We used a novel episodic flanker task that turns the famous perceptual flanker task inward, presenting memory lists followed by probes that asked whether a cued letter had appeared in the same position in the memory list. Like the perceptual flanker task, we manipulated distance to measure the sharpness of the focus of attention on memory, and compatibility to measure the resistance to distraction. To measure the time-course of focusing, we presented a cue indicating the probed position in the interval between the list and the probe and varied the interval between the cue and the probe (0, 250, 500, 750 ms). The main questions were whether the focus would become sharper and resistance to distraction would become stronger as cue-probe delay increased. Experiments 1a and 1b showed strong distance effects and strong cue-probe interval effects but no reliable interaction between them. Experiments 2a and 2b showed robust compatibility effects and cue-probe interval effects but no interaction between them. Thus, there is no evidence that the sharpness of the focus increases and little evidence that the resistance to distraction improves over time. The robust reduction in response time and slight increase in accuracy with cue-probe interval may reflect the time-course of orienting to the cued position in the memory list prior to focusing on the item it contains.

Different (key)strokes for different folks: How standard and nonstandard typists balance Fitts' law and Hick's law.

Fine motor skills like typing involve a mapping problem that trades Fitts' law against Hick's law. Eight fingers have to be mapped onto 26 keys. Movement time increases with distance, so Fitts' law is optimized by recruiting more fingers. Choice difficulty increases with the number of alternatives, so Hick's law is optimized by recruiting fewer fingers. The effect of the number of alternatives decreases with consistent practice, so skilled typists achieve a balance between Fitts' law and Hick's law through learning. We tested this hypothesis by comparing standard typists who use the standard QWERTY mapping consistently with nonstandard typists who use fewer fingers less consistently. Typing speed and accuracy were lower for nonstandard typists, especially when visual guidance was reduced by removing the letters from the keys or covering the keyboard. Regression analyses showed that accommodation to Fitts' law (number of fingers) and Hick's law (consistency) predicted typing speed and accuracy. We measured the automaticity of typing in both groups, testing for hierarchical control in 3 tasks: word priming, which measures parallel activation of keystrokes, keyboard recall, which measures explicit knowledge of letter locations, and hand cuing, which measures explicit knowledge of which hand types which letter. Standard and nonstandard typists showed similar degrees of hierarchical control in all 3 tasks, suggesting that nonstandard typists type as automatically as standard typists, but their suboptimal balance between Fitts' law and Hick's law limits their ability to type quickly and accurately. (PsycINFO Database Record

What skilled typists don't know about the QWERTY keyboard.

We conducted four experiments to investigate skilled typists' explicit knowledge of the locations of keys on the QWERTY keyboard, with three procedures: free recall (Exp. 1), cued recall (Exp. 2), and recognition (Exp. 3). We found that skilled typists' explicit knowledge of key locations is incomplete and inaccurate. The findings are consistent with theories of skilled performance and automaticity that associate implicit knowledge with skilled performance and explicit knowledge with novice performance. In Experiment 4, we investigated whether novice typists acquire more complete explicit knowledge of key locations when learning to touch-type. We had skilled QWERTY typists complete a Dvorak touch-typing tutorial. We then tested their explicit knowledge of the Dvorak and QWERTY key locations with the free recall task. We found no difference in explicit knowledge of the two keyboards, suggesting that typists know little about key locations on the keyboard, whether they are exposed to the keyboard for 2 h or 12 years.