Detection of small orientation changes and the precision of visual working memory

Abstract

We investigated the precision of orientation representations with two tasks, change detection and recall. Previously change detection has been measured only with relatively large orientation changes compared to psychophysical thresholds. In the first experiment, we measured the observers' ability (d') to detect small changes in orientation (5-30°) with 1-4 Gabor items. With one item even a 10° change was well detected (average d'=2.5). As the amount of change increased to 30°, the d' increased to 5.2. When the number of items was increased, the d's gradually decreased. In the second experiment, we used a recall task and the observers adjusted the orientation of a probe Gabor to match the orientation of a Gabor held in the memory. The standard deviation (s.d.) of errors was calculated from the Gaussian distribution fitted to the data. As the number of items increased from 1 to 6, the s.d. increased from 8.6° to 19.6°. Even with six items, the observers did not make any random adjustments. The results show a square root relation between the d'/s.d. and the number of items. The d' in change detection is directly proportional to the square root of (1/n) and the orientation change. The increase of the s.d. in recall task is inversely proportional to square root of (1/n). The results suggest that limited resources and precision of representations, without additional assumptions, determine the memory performance.

Independent sources of anisotropy in visual orientation representation: a visual and a cognitive oblique effect

“…It has been shown that the ability to detect a change of the spatial frequency of a Gabor gating after a memory delay degraded with increasing number of stimuli (Wright et al 2000;Wilken and Ma 2004). In orientation reproduction tasks in which subjects had to reproduce a probe orientation within an array of previously presented orientation stimuli, a monotonic was observed similar to our study (Wilken and Ma 2004;Salmela and Saarinen 2013). In contrast to our prediction (see "Introduction"), the increasing delay time in experiment 1 had no effect on orientation accuracy.…”

“…c σ (modeling the SD of the orientation error) for all subjects plotted against stimulus orientation as predicted from the GAMLSS model applied to the data set of experiment 1. Line colors correspond to number of presented targets 1: black, 2: red, 3: green and 4: blue and different line shapes correspond to different presentation times (1 s: solid, 2 s: log-dashed, 5 s: two-dashed and 7 s: dotted) (color figure online) of visual orientations from working memory, target presentation time was either varied depending on the number of items in the array assuming a constant viewing time per item (Salmela and Saarinen 2013) or was constant independent of the number of items in the array to be remembered (Wilken and Ma 2004). In our first experiment, we kept this time constant.…”

Attentional Control via Parallel Target-Templates in Dual-Target Search

“…The task used orientation stimuli that were designed to: (a) equate the discriminability of two targets that could be separately cued, (b) elicit variation in the accuracy of responses and RTs as a function of set size and (c) maximise competitive interactions within VWM by requiring observers to search for targets defined by different values from a single feature-dimension [24], [28]. Displays contained rectangular stimuli that subtended 2.5° by 0.5° of visual angle.…”

“…Recent research, however, has revealed that increasing the number of objects in VWM reduces the precision with which they are maintained [22]–[24]. In the standard signal detection framework, d’ is determined by two parameters; the distance between the distributions associated with the target and the distractors and the common standard deviation of these distributions [31].…”

“…Data from Change Detection tasks has shown that the precision of items in VWM decreases as a function of the number of to-be-remembered objects [22]–[24]. Generalising this finding to search, predicts a reduction in the quality of the information used to categorise objects in the display when observers have to remember more than one object.…”