Our latest work: on attention, letter processing, memory

The below is what we’ll be presenting at EPC 2017 (the Experimental Psychology Conference of Australasia) near Newcastle, Australia. The topics are attention and letter processing, word processing, and visual working memory.

When do cues work by summoning attention to a target and when do they work by binding to it?

Alex Holcombe & Charles Ludowici

In exogenous cuing experiments, a cue such as a circle flashes at one of several locations, any of which might contain a target soon after. Accuracy is near chance when the cue is presented simultaneously with the target, but improves rapidly for longer lead times between the cue and the target. The curve tracing this out has positive skew, consistent with a rapid (~80 ms, with variability) shift of attention.

We will report evidence that exogenous cues can also facilitate performance by binding to a buffered representation of the target, obviating the need for attention to shift to the location. We presented rapid streams of letters (RSVP) concurrently in multiple locations. A random letter in a single stream was briefly cued by a circle and participants tried to report the cued letter. Analysis of the errors reveals binding, as indicated by 1) participants reporting non-targets that were presented shortly before the cue nearly as often as items after the cue; 2) the distribution of the times of the non-targets reported was mirror-symmetric rather than positively skewed. Our results suggest that more than eight letters were activated and buffered simultaneously before the cue even appears.

Can SFT identify a model’s processing characteristics when faced with reaction time variability?

Charles Ludowici, Chris Donkin, Alex Holcombe

The Systems Factorial Technology (SFT) analysis technique, in conjunction with appropriately-designed behavioural experiments, can reveal the architecture, stopping rule and capacity of information processing systems. Researchers have typically applied SFT to simple decisions with little variability in processing demands across stimuli. How effective is SFT when the stimuli vary in their processing demands from trial-to-trial? For instance, could it be used to investigate how humans process written words? To test SFT’s performance with variable stimuli, we modelled parallel limited-, unlimited- and super-capacity systems using linear ballistic accumulator (LBA) models. The LBA models’ parameters were estimated for individual participants using data from a lexical decision experiment – a task that involved a set of stimuli with highly variable, stimulus-specific response times. We then used these parameters to simulate experiments designed to allow SFT to identify the models’ capacities, architecture and stopping rule. SFT successfully identified system capacity with <600 trials per condition. The probability of correctly identifying the LBA’s architecture and stopping rule increased with the number of trials per condition. However, even with 2000 trials per condition (8000 trials in total), the power of these tests did not exceed .6. SFT appears promising for investigating the processing of stimuli sets with variable processing demands.

Capacity limits for processing concurrent briefly presented words

Kimbra Ransley, Sally Andrews, and Alex Holcombe

Humans have a limited capacity to identify concurrent briefly-presented targets.  Recent experiments using concurrent rapid serial visual presentation (RSVP) of letters have documented that the direction of reading affects which of two horizontally-displaced streams is prioritised.  Here, we investigate whether the same pattern of prioritisation occurs when participants are asked to identify two horizontally displaced words.  Using a stimulus where two words are briefly presented at the same time (not embedded in an RSVP stream), and the location of one of the words is subsequently cued, we do not find evidence of prioritisation in the direction of reading. Instead, we observed a right visual field advantage, that was not affected by whether participants were told which word to report immediately, or after a 200ms delay.  We compare these results with results from an experiment where the two words are embedded in an RSVP stream. These experiments provide insight into the conditions in which hemispheric differences rather than reading-related prioritisation drives visual field differences, and may have implications for our understanding of visual processes that operate when one must identify and remember multiple stimuli, such as when reading.

“Memory compression” in visual working memory depends on explicit awareness of statistical regularities.

William Ngiam, James Brissenden, and Edward Awh

Visual working memory (WM) is a core cognitive ability that predicts broader measures of cognitive ability. Thus, there has been much interest in the factors that can influence WM capacity. Brady, Konkle & Alvarez (2009) argued statistical regularities may enable larger number of items to be maintained in this online memory system. In a WM task that required recall of arrays of colours, they included a patterned condition in which specific colours were more likely to appear together. There was a robust improvement in recall in this condition relative to one without the regularities. However, this is inconsistent with multiple other studies that have found no benefit of exact repetitions of sample displays in similar working memory tasks (e.g., Olson and Jiang, 2004). We replicated the benefit Brady et al. observed in the patterned condition in two separate studies, but we obtained larger samples of subjects and included an explicit test of memory for the repeated colours pairs. Critically, memory compression effects were observed only in the subset of subjects who had perfect explicit recall of the colour pairings at the end of study. This effect may be better understood as an example of paired associate learning.

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