Dr Michael Pilling

Two experiments investigate how absolute and relative spatial cues influence perceptual comparisons between visual short-term memory (VSTM) and current vision. The core question concerned the role of task demands in this process. Two tasks were given across two experiments, differing in the extent they required object-level comparisons. Experiment 1, a feature comparison task, required reporting if any new colour was present in the second of two interleaved displays of four colours inside a surround; Experiment 2, an object comparison task, required report of any changes in colour-shape pairings in the second of two interleaved displays of four coloured shapes in a surround. Absolute and relative spatial organization was manipulated in both experiments by presenting compared displays on the same or contralateral sides, and by having the second display items in the same locations within the surround, in new locations, or repositioned into previous locations of other items. In sensitivity, both tasks showed an advantage for absolute spatial cues, but only the object task showed an advantage for relative spatial cues. In bias, both tasks were similarly influenced by both absolute and relative cues. Results suggest relative spatial cues are always available but only used when making object-level comparisons.

Two studies examine the circumstances in which a singleton object, defined by a unique feature-change rate within a display, guides attention in visual search. Participants searched for a static vertical/horizontal white target bar amidst tilted distractors. All bars were contained inside surround coloured shapes with periodically oscillating features. In Experiment 1, displays consisted of surrounds with abrupt (discrete) or continuous (smooth) changes between two values (red-blue, square-diamond). For discrete displays, target surrounds did not guide attention when uniquely faster-oscillating than distractor surrounds but did so in smooth displays. For a unique slower-oscillating target surround the opposite guidance pattern was found across discrete and smooth displays. In Experiment 2, displays had a combination of discrete and smooth change distractors. Here only unique slower oscillating discrete surrounds guided attention. No guidance was found for smooth surrounds. Findings suggest that faster oscillations are masked by higher-frequency harmonic signals from slower changing discrete items, and there is attentional prioritisation of discrete over smooth changes.

Objectives: 
The purpose of the current study was to investigate the potential of pupillometry to provide an objective measure of competition between tinnitus and external sounds during a test of auditory short-term memory.

Design: 
Twelve participants with chronic tinnitus and twelve control participants without tinnitus took part in the study. Pretest sessions used an adaptive method to estimate listeners’ frequency discrimination threshold on a test of delayed pitch discrimination for pure tones. Target and probe tones were presented at 72 dB SPL and centered on 750 Hz±2 semitones with an additional jitter of 5 to 20 Hz. Test sessions recorded baseline pupil diameter and task-related pupillary responses (TEPRs) during three blocks of delayed pitch discrimination trials. The difference between target and probe tones was set to the individual’s frequency detection threshold for 80% response-accuracy. Listeners with tinnitus also completed the Tinnitus Handicap Inventory (THI). Linear mixed effects procedures were applied to examine changes in baseline pupil diameter and TEPRs associated with group (tinnitus versus control), block (1 to 3) and their interaction. The association between THI scores and maximum TEPRs was assessed using simple linear regression.

Results: 
Patterns of baseline pupil dilation across trials diverged in listeners with tinnitus and controls. For controls, baseline pupil dilation remained constant across blocks. For listeners with tinnitus, baseline pupil dilation increased on blocks 2 and 3 compared with block 1. TEPR amplitudes were also larger in listeners with tinnitus than controls. Linear mixed effects models yielded a significant group by block interaction for baseline pupil diameter and a significant main effect of group on maximum TEPR amplitudes. Regression analyses yielded a significant association between THI scores and TEPR amplitude in listeners with tinnitus.

Conclusions: 
Our data indicate measures of baseline pupil diameter, and TEPRs are sensitive to competition between tinnitus and external sounds during a test of auditory short-term memory. This result suggests pupillometry can provide an objective measure of intrusion in tinnitus. Future research will be required to establish whether our findings generalize to listeners across a full range of tinnitus severity.

A major role for visual short-term memory (VSTM) is to mediate perceptual comparisons of visual information across successive glances and brief temporal interruptions. Research that has focused on the comparison process has noted a marked tendency for performance to be better when participants are required to report a difference between the displays rather than report the absence-of-a-difference (i.e. a sameness). We refer to this performance asymmetry as report-difference superiority (RDS). It has been suggested that RDS reflects the operation of a reflexive mechanism that generates a mismatch signal during the comparison of visual input with information maintained in VSTM. This bottom-up mechanism therefore gives evidence for the presence of a feature change but not for the absence of such a change; consequently a sameness is harder to detect than a difference between two displays (Hyun et al. 2009). We test this explanation, and determine whether by itself it is a sufficient explanation of the RDS. In a delayed comparison task we find the RDS effect is most prevalent when items retain the same display locations, however the effect does persist even when compared item locations were scrambled across memory and test arrays. However, with a conjunction task this scrambling of locations was effective in wholly abolishing the RDS effect. We consider that the RDS effect is a consequence of local comparisons of features, as well as global statistical comparisons.

Hoerl and McCormack (H&M) risk misleading about the cognitive underpinnings of the belief in a privileged now-moment because they do not explicitly acknowledge that the sense of existing in the now-moment is an intrinsically temporally dynamic one. The sense of happening that is exclusive to the now-moment is a better candidate for the source of belief in a privileged now.

Two experiments examined the effect of Object Substitution Masking (OSM) on the perceptual errors in reporting the orientation of a target. In Experiment 1 a four-dot trailing mask was compared with a simultaneous-noise mask. In Experiment 2, the four-dot and noise masks were factorially-varied. Responses were modelled using a mixture regression-model and Bayesian-inference to deduce whether the relative impacts of OSM on guessing and precision were the same as those of a noise mask, and thus whether the mechanism underpinning OSM is based on increasing noise rather than a substitution process. Across both experiments, OSM was associated with an increased guessing-rate when the mask trailed target offset, and a reduction in the precision of the target representation (although the latter was less reliable across the two experiments). Importantly, the noise mask also influenced both guessing and precision, but in a different manner, suggesting that OSM is not simply caused by increasing noise. In Experiment 2 the effects of OSM and simultaneous-noise interacted, suggesting the two manipulations involve common mechanisms. Overall results suggest that OSM is often a consequence of a substitution process, but there is evidence that the mask increases noise levels on trials where substitution doesn’t occur. 

Attention is known to be sensitive to the temporal structure of scenes. We initially tested whether feature synchrony, an attribute with potential special status because of its association with objecthood, is something which draws attention. Search items were surrounded by colours which periodically changed either in synchrony or out-of synchrony with periodic changes in their shape. Search for a target was notably faster when the target location contained a unique synchronous feature change amongst asynchronous changes. However, the reverse situation produced no search advantage. A second experiment showed that this effect of unique synchrony was actually a consequence of the lower rate of perceived flicker in the synchronous compared to the asynchronous items, not the synchrony itself. In our displays it seems that attention is drawn towards a location which has a relatively low rate of change. Overall, the pattern of results suggested the attentional bias we find is for relative temporal stability. Results stand in contrast to other work which has found high and low flicker rates to both draw attention equally [Cass, J., Van der Burg, E., & Alais, D. (2011). Finding flicker: Critical differences in temporal frequency capture attention. Frontiers in Psychology, 2, 320]. Further work needs to determine the exact conditions under which this bias is and is not found when searching in complex dynamically-changing displays.

Design: Response functions for six normal listeners on a delayed pitch discrimination task were contrasted in three conditions designed to manipulate attention in the presence and absence of simulated tinnitus: (1) no-tinnitus, (2) ignore-tinnitus, and (3) attend-tinnitus.

Results: Delayed pitch discrimination functions were more variable in the presence of simulated tinnitus when listeners were asked to divide attention between the primary task and the amplitude of the tinnitus tone.

Conclusions: Changes in the variability of auditory short-term memory may provide a novel means of quantifying the level of intrusion associated with the tinnitus percept during listening.

Bioethics; Human participants

Baron (2015) in this issue nicely identifies some of the issues the scientist faces in gaining ethical approval for their research, as well as offering a credible alternative to address these problems. We have made a number of observations – both from our own experiences and from those of our colleagues at various institutions – on the ethical approval process. Ethics is often a source of frustration for the research scientist; it can be time consuming, it operates as a bottleneck in the research process – by extension – it is arguably an impediment to scientific progress. The process of obtaining ethical acceptance is often a wearisome one for scientists and a frequent source of complaint. The impression is given that ethical panels tend to tolerate rather than support research on human participants. Some seem to operate from a starting principle of research on human participants' being an exploitative one, i.e., one in which, without the guardianship provided by the panels, scientists would frequently, knowingly or unknowingly, infringe upon the welfare of individual participants. Indeed, in the UK the National Research Ethics Service of the National Health Service seems to explicitly pledge such a role in affirming its service exists to protect the ‘rights, safety, dignity and well-being of research participants’ as its primary concern. We believe that the other ethical committees of different institutions may espouse similar views. This starting point of apparent antagonism between the scientist and ethics review panel is not a helpful one and is a source of many of the frustrations that scientists experience. Baron further argues that ethics review board members often fail to apply the parameters to judge ethical components in any constant manner; even where consistency is evident this is never done in terms of any objective analysis of expected utility-loss. This problem has been recognised before in critiques of the ethical review process. In particular Zimbardo (1973) – after his Stanford Prison Experiment – noted how ethics reviewers tend to make decisions using a relative (contingent) ethical principle, one which has potential to be used arbitrarily. It is notable that in Universities at least, the application of ethical principle seems to be something uniquely applied to research activities. No such ethical principle or process applies to other contexts, for example teaching. Thus the same stimulus set and experimental task can be conducted for educational or demonstration purposes in the teaching room. If the same experiment is done as part of a research activity then it suddenly falls into the domain of the ethics board and requires a whole set of protocols to follow and approvals to be obtained. It is not clear how same intervention (same stimuli/experiment) requires the application of two different set of rules, nor what is special about research per se which makes it a unique source of formal ethical concern.

We agree with Baron's point that the ethics board reviewer may make systematic errors in exaggerating low probability risks. In our personal view and experience of working at various institutions, we conservatively estimate to have each tested well over 2000 participants, either directly as a researcher or indirectly through supervising students' research, but either of us has yet had any encounter of a situation where a participant displayed an unanticipated or unpleasant reaction to an experimental manipulation or stimulus presentation. It is ironic that in most cases the research scientist themselves is the one best placed to assess the most likely risks of an experiment they are conducting; the ethical review panellists are often making judgements on things which are outside of their field of experience and expertise.

Baron goes on to propose that ethics board members be trained in decision making and statistics and be taught to bring such rules of logic to the ethical review process. However, such approach has the danger of becoming too formalised. It could ultimately lead to board members being replaced with an automated computer algorithm or expert system to make ethical decisions. Probably, as researchers we won't like to see this and most would like to retain some level of human element in the ethical decision process even despite the flaws and frustrations we have highlighted.

In object substitution masking (OSM) a surrounding mask (typically comprising of 4 dots) onsets with a target but lingers after offset; under such conditions, the ability to perceive the target can be significantly reduced. OSM was originally claimed to occur only when a target was not the focus of attention, for instance, when embedded in an array of distractors (Di Lollo, Enns, & Rensink, 2000). It was argued that the distractors influenced the time taken for focal attention to reach the target. Some recent work, however, failed to find any such distractor influence; the effect of mask duration was found to be independent of set size when steps were taken to avoid ceiling effects in the smallest set size condition (Argyropoulos, Gellatly, Pilling, & Carter, 2013; Filmer, Mattingley, & Dux, 2014). In 3 experiments, we repeatedly found that set size manipulations can interact with mask duration (in which neither ceiling nor floor effects are evident), with the effect of the mask on target perceptibility being amplified according to the number of distractor items. However, a further experiment (Experiment 4) showed that crowding by nearby distractors was actually responsible for this "set size" effect. When decoupled from crowding, set size alone did not interact with masking, though it did influence overall accuracy. Thus, the presence of distractors does influence OSM, but not in the way originally assumed by Di Lollo and colleagues in their model. The Crowding × OSM interaction suggests that the 2 phenomena involve partly overlapping mechanisms.

Object substitution masking (OSM) is used in behavioral and imaging studies to investigate processes associated with the formation of a conscious percept. Reportedly, OSM occurs only when visual attention is diffusely spread over a search display or focused away from the target location. Indeed, the presumed role of spatial attention is central to theoretical accounts of OSM and of visual processing more generally (Di Lollo, Enns, & Rensink, Journal of Experimental Psychology: General 129:481-507, 2000). We report a series of five experiments in which valid spatial precuing is shown to enhance the ability of participants to accurately report a target but, in most cases, without affecting OSM. In only one experiment (Experiment 5) was a significant effect of precuing observed on masking. This is in contrast to the reliable effect shown across all five experiments in which precuing improved overall performance. The results are convergent with recent findings from Argyropoulos, Gellatly, and Pilling (Journal of Experimental Psychology: Human Perception and Performance 39:646-661, 2013), which show that OSM is independent of the number of distractor items in a display. Our results demonstrate that OSM can operate independently of focal attention. Previous claims of the strong interrelationship between OSM and spatial attention are likely to have arisen from ceiling or floor artifacts that restricted measurable performance.

Object-substitution masking (OSM) occurs when a mask, such as four dots that surround a brief target item, onsets simultaneously with the target and offsets a short time after the target, rather than simultaneously with it. OSM is a reduction in accuracy of reporting the target with the temporally trailing mask, compared with the simultaneously offsetting mask. It has been thought that OSM occurs only if attention cannot be rapidly focused, or prefocused, on the target location. One line of evidence for this is a reported interaction between target display set size and the duration of the trailing mask. We analyze the evidence for this interaction and suggest it occurs only as an artifact of data being compressed by a ceiling effect. We report six experiments that support this interpretation by showing that the interaction is always absent unless a ceiling effect is induced. We go on to analyze other evidence to support the notion that attention modulates OSM, and argue that in each case, the data either reflect a ceiling effect or can be explained in another way. Our data and our analyses of the existing literature have strong implications for how OSM should be conceptualized. (PsycINFO Database Record (c) 2012 APA, all rights reserved).

One of the processes determining object substitution masking (OSM) is thought to be the spatial competition between independent object file representations of the target and mask (e.g., Kahan & Lichtman, 2006). In a series of experiments, we further examined how OSM is influenced by this spatial competition by manipulating the overlap between the surfaces created by the modal completion of the target (an outline square with a gap in one of its sides) and the mask (a four-dot mask). The results of these experiments demonstrate that increasing the spatial overlap between the surfaces of the target and mask increases OSM. Importantly, this effect is not caused by the mask interfering with the processing of the target features it overlaps. Overall, the data indicate, consistent with Kahan and Lichtman, that OSM can arise through competition between independent target and mask representations.

At any given moment, our awareness of what we 'see' before us seems to be rather limited. If, for instance, a display containing multiple objects is shown (red or green disks), when one object is suddenly covered at random, observers are often little better than chance in reporting about its colour (Wolfe, Reinecke, & Brawn, Visual Cognition, 14, 749-780, 2006). We tested whether, when object attributes (such as colour) are unknown, observers still retain any knowledge of the presence of that object at a display location. Experiments 1-3 involved a task requiring two-alternative (yes/no) responses about the presence or absence of a colour- defined object at a probed location. On this task, if participants knew about the presence of an object at a location, responses indicated that they also knew about its colour. A fourth experiment presented the same displays but required a three-alternative response. This task did result in a data pattern consistent with participants' knowing more about the locations of objects within a display than about their individual colours. However, this location advantage, while highly significant, was rather small in magnitude. Results are compared with those of Huang (Journal of Vision, 10(10, Art. 24), 1-17, 2010), who also reported an advantage for object locations, but under quite different task conditions.

The perceptibility of a flickering central bar can be dramatically reduced by the presence of two flanking bars presented in counterphase. This phenomenon, known as the 'standing wave illusion', has been suggested to involve local edge interactions (Macknik et al, 2000 Proceedings of the National Academy of Sciences of the USA 97 7556 - 7560). High-level re-entrant mechanisms have also been implicated. Enns (2002, Psychonomic Bulletin & Review 9 489-496) reports an association between the reported viability of the centre bar and its similarity in shape with the flanking bars. We find that this relationship between shape similarity and reported visibility seems to be contingent on the degree of experienced apparent motion. When target duration is shortened, so reducing apparent motion, reports of visibility reflect the amount of abutting contour. In a further experiment we find that luminance discriminations of the centre bar are related to the amount of abutting contour not to shape similarity. This is despite experiment 3 being conducted at stimulus durations for which experiment 2 visibility ratings indicated that shape similarity is important and contour is not. We suggest that this perceived motion may be the factor mediating shape 'effects' in the reported visibility task. We propose that the absence of such shape effects in the discrimination task may be because the task provides an objective measure of visibility that is immune to bias from perceived motion. We also speculate that while target luminance information may be immune to masking resulting from perceived motion, it may be subject to masking due to lateral inhibition.