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Proneness to psychosis and selection of objects of visual attention: individual differences in visual marking
Personality and Individual Differences 36 (2004) 1771–1779 www.elsevier.com/locate/paid
Proneness to psychosis and selection of objects of visual attention: individual differences in visual marking Oliver J. Mason a
a,*
, Helen Booth b, Christian Olivers
b
Department of Clinical and Health Psychology, University College London, Gower Street, London WC1N 6BT, UK b School of Psychology, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK Received 13 January 2003; received in revised form 15 May 2003; accepted 1 July 2003
Abstract Deficits in early visual attention and perceptual organisation have frequently been shown to associate with both poor pre-morbid schizophrenia and those at a greater putative risk of psychosis. The nature of the deficit is unclear. The present study investigated the relationship between speed of visual marking and proneness to psychosis. 20 males and 20 females completed several tasks assessing speed of selection and deselection of visual objects. As predicted, negative schizotypy was associated with poorer marking in males, but socially desirable responding potentially confounded this result. In addition, impulsive non-conformity swas associated with poorer visual marking, more prominently in females. These results are discussed in relation to possible mechanisms by which psychosis-proneness and impulsivity may restrict the top–down influences operating on early visual attention. 2003 Elsevier Ltd. All rights reserved. Keywords: Psychosis-proneness; Impulsivity; Visual attention
1. Introduction A growing body of evidence suggests that various deficits in early visual attention are associated both with some forms of schizophrenia, and with a psychometrically greater risk of putative psychosis measured using questionnaires. With respect to schizophrenia, research findings are necessarily complicated by the exact nature of the task used, and by the sample. Studies of relatively late aspects of visual attention such as the formation of gestalt (Chey & Holzman, 1997) and global visual sensory store processing (Knight, Manoach, Elliott, & Hershenson, 2000) have *
Corresponding author. Tel.: +121-414-3836; fax: +121-414-4913. E-mail address: [email protected] (O.J. Mason).
0191-8869/$ - see front matter 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.paid.2003.07.015
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generally found these to be intact. However, patients with a more chronic illness, greater cognitive disorganisation or poorer pre-morbid status (all of which indicate a higher genetic loading) have been shown to perform more poorly on perceptual grouping tasks (Silverstein, Kovacs, Corry, & Valone, 2000), and also fail to utilise top–down information in the form of added contextual cues (Silverstein et al., 1996a). The evidence supports the compromise of early attentional processes in those who have poorer pre-morbid function or go on to develop a more chronic illness; however, medication remains a potential confound to all studies in this area as it is precisely these patients who have received greater and longer treatment. Those studies that use non-clinical populations have measured differences in so-called schizotypal individual differences (Obiols, Garcia-Domingo, de Trincheria, & Domenech, 1993; Watson & Tipper, 1997; Rawlings & Goldberg, 2001). This research strategy has the potential advantage of both highlighting paradigms meriting further investigation in clinical conditions, as well as identifying markers of potential aetiological significance to psychosis, rather than deficits that are the consequence of it. Participants are also free of the potentially damaging effects of a psychiatric history including prolonged neuroleptic use. The current study uses this strategy to investigate individual differences in neuro-cognition that are of potential relevance to psychosis research. The majority of studies of cognitive processes in both patients and schizotypal individuals have used what might be termed multi-componential tasks that contain demands on stimulus selection, memory and sustained attention. Though of relevance to the argument that a deficit in ÔattentionÕ as a whole forms part of the diathesis to psychosis, tasks assessing latent inhibition, sustained attention and figure-ground discrimination are frequently less able to specify the cognitive neuropsychological nature of such a deficit. However, some researchers have suggested that at least part of the difficulty for schizophrenic patients is a problem of Ôdisregarding the irrelevant stimulusÕ (Braff, 1993; Schwartz & Evans, 1999). One concern has been to identify whether this is a limitation imposed by stimulus-driven (bottom–up) or knowledge-based (top–down) processes. Silverstein, Matteson, and Knight (1996b) found that schizophrenics could not use contextual cues to select auditory information but could use acoustic ones suggesting top–down limitations. Similar studies have extended this finding to visual patterns (Silverstein et al., 1996a; Silverstein, Bakshi, Chapman, & Nowlis, 1998). Both results suggest that top–down processes may be impaired in acute schizophrenia though the nature of this deficit is at present hard to specify. The present study attempts to clarify the nature of differences in top–down processing operating at an early stage of visual attention. One approach to the cognitive neuropsychology of visual attention that has received extensive attention has been termed visual marking (Watson & Humphreys, 1997). Watson and HumphreysÕ task aims to investigate how old objects are de-prioritised, so aiding efficient selection of new objects. Watson and Humphreys had participants search for a blue letter H among green Hs and blue As. There were three main conditions. In the standard conjunction search task, a target (when present) appeared among green H and blue A distractor items. In the standard singlefeature search condition, the blue H target had to be detected among blue letter A distractors. In the third, preview condition there was a temporal delay of 1000 ms between the onset of an initial subset of distractors (green Hs) and the onset of the remainder of the search items (blue A distractors and, on target-present trials, a blue H). Display sizes varied between 2 and 16 items. Interestingly, the slope of the search function for the preview condition was similar to that in the single-feature baseline and it was substantially less than that found in the color-form conjunction
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condition. The data show that, in the preview condition, the old green distractors had minimal impact on search. Converging results with the visual marking paradigm suggest that this process is a resource-limited process requiring attention control and not simply an automatic one (Watson & Humphreys, 2000; Olivers, Watson, & Humphreys, 1999). Proponents of visual marking argue that its active application makes sense in evolutionary terms, as marking would enable changes in complex environments (such as predator movement) to be efficiently monitored. Recent work has described the neuroanatomical basis of marking in both fMRI (Pollmann et al., 2003) and ERP studies (Jacobsen, Humphreys, Schroger, & Roeber, 2002). Activation of a frontal-parietal network is seen in all studies, with an initial locus in the central frontal areas, with greater activation on the left side in one study (Jacobsen et al., 2002). The time course of frontal activation (350–750 ms) is consistent with behavioural data on the stimulus onset asynchrony required for marking to occur and substantiates the Ôactive suppressionÕ of visual objects as an account of the phenomenon. Study of clinical phenomena associated with marking deficits has been limited, though one unpublished study has implicated poor marking associated with attention deficit disorder in adolescents (Humphreys, personal communication). Detailed analysis pointed to specific difficulty inhibiting an early (and inappropriate) response to the distracter set. We do not suggest that the attention deficit associated with psychosis-proneness would necessarily take this form. However, it is probable that there are several routes to deficits in visual marking associated with different neuropsychological impairments. The study aimed to delineate the nature of the attention deficit involved with psychosis-proneness further using the visual marking paradigm. A feature of contemporary measures of psychosis-proneness is their multi-dimensional nature (Raine, 1991; Mason, Claridge, & Jackson, 1995)––typically containing, at the least, measures of positive and negative schizotypy, as well as cognitive disorganisation. The measure used here also contains a fourth component called impulsive non-conformity that combines elements of psychoticism (Eysenck & Eysenck, 1976) with hypomania and borderline personality disorder. While this development to measurement has helped clarify the diversity of findings with proneness measures, it renders specific hypothesis testing challenging. Without prior findings it is difficult to specify which factor might relate to a particular deficit such as one of visual marking. However, several previous studies support both an attention deficit (Chen, Hsiao, & Lin, 1997) and poor somatosensory discrimination (Lenzenweger, 2000) in anhedonic individuals and those with chronic negative symptoms. In keeping with a range of findings of reduced parietal activity as a basis for negative symptoms (e.g. Tamminga, Buchannan, & Gold, 1998) we hypothesised negative schizotypy, in the form of introvertive anhedonia (Mason et al., 1995), to relate to visual marking ability as this has a parietal basis. However, it is difficult to rule out the other factors as some shared variance is frequently identified, and indeed a case can be made for an inhibitory deficit for any factor.
2. Method 2.1. Participants Forty undergraduate students (20 male and 20 female) at the University of Birmingham completed the measures of visual marking and psychosis-proneness. Ages ranged from 17 to 25
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(mean ¼ 19.0, s.d. ¼ 4.3). The participants were not informed of the purpose of the study. All reported having normal or corrected-to-normal vision and normal colour vision. 2.2. Design The design for the visual marking task was similar to that of Watson and Humphreys (1997) described in Section 1. There were three visual search conditions: single feature, conjunction and preview. Participants were presented with nine blocks of twenty-four trials: within blocks 1–3, 4–6 and 7–9, each condition appeared once in randomised order. Overall, participants were exposed to each condition three times. 2.3. Stimuli and apparatus All stimuli were presented on a sVGA monitor controlled by a PC/Mach64 VGA graphics card. The target was always present (light blue H) and the distracters were light green Hs and light blue As. In the conjunction and preview conditions, half the distracters were light green Hs and half were light blue As. In the preview condition there was a 1000 ms pause between the appearance of the first distracters (green Hs) and the presentation of the second set of distracters (blue As). The stimuli letters were 4 mm wide and 8 mm high. The search displays were generated by randomly positioning each item in the middle of cells making up an invisible 10 · 10 matrix. The overall matrix size was 137 mm wide by 135 mm high as used by Olivers et al. (1999). There were four new items in all trials making a total of eight items in preview and conjunction conditions. 2.4. Procedure Participants completed the visual marking task following instructions presented on the screen. The screen was viewed from a distance of 70 cm. On each trial a white fixation cross (1.3 mm · 1.3 mm) appeared in the centre of the screen for 1000 ms. Following this, the search display was presented and remained until the participant responded, or a time-out period of 5 s concluded. Responses were made by pressing the left-hand mouse key with the right index finger. Participants were required to press once as soon as they saw the target in the display. The display then disappeared and the outline of a matrix (5 · 5 circles) appeared on the screen against a black background––the circles represented possible locations for where the target had appeared. Participants were asked to move the mouse so that the screen arrow pointed to approximately where the target had appeared, and press once again. The first response was designed to measure reaction times, while the second provided a check of accuracy. Participants were asked to respond as quickly as possible, but to make as few errors as possible. If participants made an error during a trial, the trial was automatically re-shown at the end of that block, so that a full set of results was obtained. The task took 15 min to complete. After a short recovery period, participants completed the following personality scales. 2.5. Psychosis-proneness scales The following scales were drawn from the O-LIFE (Mason et al., 1995). Unusual experiences contains items describing perceptual aberrations, magical thinking and hallucinations. It is phenomenologically related to positive symptoms of psychosis. Cognitive
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disorganisation describes aspects of poor attention and concentration as well as poor decisionmaking and social anxiety. It can be seen to reflect thought disorder and other disorganised aspects of psychosis. Introvertive anhedonia describes a lack of enjoyment from social and physical sources of pleasure as well as avoidance of intimacy. It can be seen to reflect so-called Ônegative symptomsÕ, or alternatively the schizoid temperament. Impulsive non-conformity contains items describing impulsive, anti-social and eccentric forms of behaviour, often suggesting a lack of self-control. Psychometric evaluation of the O-LIFE has shown it to have good test–retest reliability (Burch, Steel, & Hemsley, 1998), internal consistency (r ¼ 0:8; Loughland & Williams, 1997) and factorial validity (Mason, 1995). An increasing literature has supported experimental findings across the range of scales with paradigms thought to reflect vulnerability to psychosis. In addition, the Lie scale was also included as a measure of socially desirable responding (Eysenck & Eysenck, 1975). 2.6. Indices of visual marking Mean reaction times were calculated for each participant in each condition from three blocks. Two indices of visual marking were calculated. The difference index was calculated by subtracting RTs in the preview condition from RTs in the conjunction condition. This difference is a measure of the superiority afforded by visual marking. A further index was calculated by dividing the difference by the single feature condition RT as a way of controlling for differences in overall speed.
3. Results 3.1. Descriptive statistics Results for both the visual marking task and personality measures are given in Table 1. By comparison to the norms provided for student populations, the males in the sample scored rather below those expected on the measure of unusual experiences and impulsive non-conformity. Results of t-tests of difference between males and females are also given in Table 1. On both unusual experiences and cognitive disorganisation, females scored more highly, in line with previous findings. Reaction times in the three experimental conditions are consistent with those previously found (Watson & Humphreys, 1997), and form the largest sample to date on this lengthy task. As expected, the single feature condition produces the lowest RTs, followed by the preview condition. In all individuals, the conjunction condition had the longest RTs, allowing a positive difference score to be calculated. No violations of normality were observed for any variable. There was a tendency for males to perform more quickly in all experimental conditions that reached significance in the conjunction condition. 3.2. Personality relationships with indices of visual marking Although two indices were calculated, results were identical for each; so only those with the difference index are reported. In practice this was due to a relatively narrow range of overall
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Table 1 Results on visual marking and psychosis-proneness measures Female Mean O-LIFE scales Unusual experiences Cognitive disorganisation Introvertive anhedonia Impulsive non-conformity Lie scale
Male s.d.
11.55 14.70 6.05 9.00 6.950
t (p-value)
Mean
s.d.
6.26 6.05 4.57 3.45
7.32 11.47 6.53 9.33
5.96 3.88 3.12 3.65
2.20 1.93 0.52 0.27
3.69
5.58
2.95
1.19 (ns)
Visual marking indices Single feature Conjunction Preview
681.4 985.4 787.0
146.3 183.3 151.4
611.7 864.4 712.2
160.2 185.6 167.0
Difference
198.3
89.4
156.7
66.7
(<0.05) (ns) (ns) (ns)
1.50 (ns) 2.22 (<0.05) 1.71 (ns) 1.66 (ns)
reaction times so that no need arose to control for differences in speed by using the simplest single feature task as a denominator. The relationships of visual marking with personality variables were examined by Pearson product-moment correlations, both for the group as a whole and separately for males and females (see Table 2). The difference index produced a trend in correlation with impulsive non-conformity (r ¼ 0:3, p ¼ 0:09) that was entirely due to the females in the sample (r ¼ 0:51, p < 0:01). The pattern of results appeared to be quite different for males: as predicted, introvertive anhedonia was significantly negatively correlated with the index. However, investigation of the male sample suggested a confounding influence of socially desirable responding (Lie scale). While the Lie scale was not significantly correlated with any other variables in females, in males it was significantly associated with impulsive non-conformity (r ¼ 0:59, p < 0:01). Although the small numbers do not permit the sample to be further subdivided, this was addressed by partial correlation, so removing the effects of social desirability statistically. When this is done, the difference index is reduced to a trend in relation to introvertive anhedonia in males (r ¼ 0:42, p ¼ 0:07), but a trend for a relationship appears with impulsive non-conformity (r ¼ 0:37, p ¼ 0:08).
Table 2 Correlations of psychosis-proneness scales with difference index
*
Scale
All
Male
Male (Lie partialled)
Female
Unusual experiences Cognitive disorganisation Introvertive anhedonia Impulsive non-conformity Lie
0.01 0.24 )0.20 )0.31 )0.02
0.24 0.08 )0.48 )0.02 )0.43
0.06 0.10 )0.42 )0.37 –
)0.19 0.24 )0.03 )0.51 0.08
p < 0:01. p < 0:1.
**
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4. Discussion The results supported the hypothesised relationship between psychosis-proneness and visual marking but were not entirely as predicted. Despite predicting associations with negative schizotypy in the form of introvertive anhedonia, reduced visual marking was more reliably associated with greater impulsive non-conformity. This finding was straightforward in the female sample but remains to be clarified in males. The hypothesised relationship with introvertive anhedonia did emerge in males but should be treated with caution because of the influence of social desirability. Potential relationships with schizotypy may be compromised by the non-representative nature (atypically low in some traits) of the male sample in the present study. We do not, therefore, regard the results in males as necessarily valid and further empirical work is clearly needed. However, gender differences are frequently seen in studies of psychosis-proneness and schizophrenia and may reflect different brain-behaviour relationships across gender (Gruzelier, 1994). The relationship of reduced visual marking with anhedonia is consistent with other results suggestive of poor attentional processing (Chen et al., 1997). Furthermore, although the evidence on visual marking is preliminary as discussed in the introduction, it is consistent with reductions in left hemisphere activation seen in a number of studies of negative schizotypy (Gruzelier & Richardson, 1994), and with the well-known hypo-frontality hypothesis. The relationship with impulsive non-conformity was somewhat less expected, though this is an aspect of psychosis-proneness that is not contained in many measures, and hence studies, in this field. However, the measureÕs clear similarity (and some content overlap) with EysenckÕs original Psychoticism scale (Eysenck & Eysenck, 1975) make it highly relevant to any study of psychosisproneness, and a finding related to poor attention is in no way at odds with his view. As Watson and Humphreys have demonstrated, visual marking involves attention-demanding top–down processes, probably in addition to automatic stimulus-property driven ones. Moreover, the magnitude of differences in visual marking (from around 68–370 ms) suggests that slower top– down processes are heavily involved. Recent empirical work (Olivers, Braithwaite, & Humphreys, in press) has clarified that there is both a search and an intercept effect––something not separated by the current paradigm using a single display size, and an admitted limitation of the study. Olivers et al. (in press) argue that the intercept effect is due to inhibiting a response to the preview, in contrast to using the preview to help guide search. It is currently unclear whether one, other or both effects are involved, though response inhibition is very clearly relevant to impulsivity. In this vein, the findings are consistent with a previously reported study of attention deficit disorder (Humphreys, personal communication), and would suggest that a greater degree of conscious control is required to suppress an early response to the distracters before the to-be-marked stimulus has occurred. Clearly further clarification is required: while the finding was clear in females, the relationship of impulsive non-conformity to differences in visual marking in males was uncertain. In part this might pertain to the rather low levels of schizotypal traits in the present study, and a wider sample of participants could help clarify the issue. The study also highlighted how socially desirable responding may be a potential confound in relationships between personality traits such as psychosis-proneness and experimental measures like visual marking. In particular, in males the relationship with introvertive anhedonia declined somewhat when socially desirable responding was controlled for, while a relationship with impulsive non-conformity appeared. As screening for the influence of social desirability has not
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hitherto been a feature of the majority of research in the field, this is strongly suggested as a desirable development.
References Burch, G. S., Steel, C., & Hemsley, D. R. (1998). Oxford-Liverpool inventory of feelings and experiences: reliability in an experimental population. British Journal of Clinical Psychology, 37, 107–108. Braff, D. L. (1993). Information processing and attention dysfunction in schizophrenia. Schizophrenia Bulletin, 19, 233– 259. Chen, W. J., Hsiao, C. K., & Lin, C. C. (1997). Schizotypy in community samples: the three-factor structure and correlation with sustained attention. Journal of Abnormal Psychology, 106(4), 649–654. Chey, J., & Holzman, P. S. (1997). Perceptual organization in schizophrenia: utilization of the Gestalt principles. Journal of Abnormal Psychology, 106(4), 530–538. Eysenck, H. J., & Eysenck, S. B. G. (1975). Manual of the eysenck personality questionnaire. London: Hodder & Stoughton. Eysenck, H. J., & Eysenck, S. B. G. (1976). Psychoticism as a dimension of personality. London: Hodder & Stoughton. Gruzelier, J. H. (1994). Syndromes of schizophrenia and schizotypy, hemispheric imbalance and sex differences: implications for developmental psychopathology. International Journal of Psychophysiology, 18(3), 167–178. Gruzelier, J. H., & Richardson, A. (1994). Patterns of cognitive asymmetry and psychosis proneness. International Journal of Psychophysiology, 18(3), 217–225. Jacobsen, T., Humphreys, G. W., Schroger, E., & Roeber, U. (2002). Visual marking for search: behavioral and eventrelated potential analyses. Cognitive Brain Research, 14(3), 410–421. Knight, R. A., Manoach, D. S., Elliott, D. S., & Hershenson, M. (2000). Perceptual organization in schizophrenia: the processing of symmetrical configurations. Journal of Abnormal Psychology, 109(4), 575–587. Lenzenweger, M. F. (2000). Two-point discrimination thresholds and schizotypy: illuminating a somatosensory dysfunction. Schizophrenia Research, 42, 111–124. Loughland, C. M., & Williams, L. M. (1997). A cluster analytic study of schizotypal trait dimensions. Personality and Individual Differences, 23, 877–883. Mason, O. (1995). A confirmatory factor analysis of the structure of schizotypy. European Journal of Personality, 9, 271–283. Mason, O., Claridge, G., & Jackson, M. (1995). New scales for the assessment of schizotypy. Personality and Individual Differences, 18, 7–13. Obiols, J. E., Garcia-Domingo, M., de Trincheria, I., & Domenech, E. (1993). Psychometric schizotypy and sustained attention in young males. Personality and Individual Differences, 14, 381–384. Olivers, C., Watson, D. G., & Humphreys, G. W. (1999). Visual marking of locations and feature maps: evidence from within dimension defined conjunctions. Quarterly Journal of Experimental Psychology, 52A, 679–715. Olivers, C., Braithwaite, J., & Humphreys, G.W. (in press). Why are responses to new targets delayed when new is prioritized? Response suppression effects in the preview paradigm. Perception and Psychophysics. Pollmann, P., Weidner, R., Humphreys, G. W., M€ uller, K., Lohmann, G., Wiggins, G. J., Olivers, C., & Watson, D. G. (2003). Separating segmentation and target detection in posterior parietal cortex––an event-related fMRI study of visual marking. NeuroImage, 18, 310–323. Raine, A. (1991). The SPQ: a scale for the assessment of schizotypal personality based on DSM-III-R criteria. Schizophrenia Bulletin, 17, 555–564. Rawlings, D., & Goldberg, M. (2001). Correlating a measure of sustained attention with a multi-dimensional measure of schizotypal traits. Personality and Individual Differences, 31, 421–431. Schwartz, B. D., & Evans, W. J. (1999). Neurophysiological mechanisms of attention deficits in schizophrenia. Neuropsychiatry, Neuropsychology and Behavioural Neurology, 12, 207–220. Silverstein, S. M., Bakshi, S., Chapman, R. M., & Nowlis, G. (1998). Perceptual Organisation of configural and nonconfigural visual patterns in schizophrenia: effects of repeated exposure. Cognitive Neuropsychiatry, 3, 209–223.
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Silverstein, S. M., Knight, R. A., Schwarzkopf, S. B., West, L. L., Osborn, L. M., & Kamin, D. (1996a). Stimulus configuration and context effects in perceptual organization in schizophrenia. Journal of Abnormal Psychology, 105(3), 410–420. Silverstein, S. M., Kovacs, I., Corry, R., & Valone, C. (2000). Perceptual organization, the disorganization syndrome, and context processing in chronic schizophrenia. Schizophrenia Research, 43(1), 11–20. Silverstein, S. M., Matteson, S., & Knight, R. A. (1996b). Reduced top–down influence in auditory perceptual organization in schizophrenia. Journal of Abnormal Psychology, 105(4), 663–667. Tamminga, C., Buchannan, R. W., & Gold, J. M. (1998). The role of negative symptoms and cognitive dysfunction in schizophrenia outcome. International Clinical Psychopharmacology, 13(suppl. 3), S21–S26. Watson, D. G., & Humphreys, G. W. (1997). Visual marking: prioritising selection for new objects by top–down attentional inhibition of old objects. Psychological Review, 104, 90–122. Watson, D. G., & Humphreys, G. W. (2000). Visual marking; evidence for inhibition using a probe-dot paradigm. Perception and Psychophysics, 62, 471–481. Watson, F. L., & Tipper, S. P. (1997). Reduced negative priming in schizotypal subjects does reflect reduced cognitive inhibition. Cognitive Neuropsychiatry, 2, 67–69.
Proneness to psychosis and selection of objects of visual attention: individual differences in visual marking Oliver J. Mason a
a,*
, Helen Booth b, Christian Olivers
b
Department of Clinical and Health Psychology, University College London, Gower Street, London WC1N 6BT, UK b School of Psychology, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK Received 13 January 2003; received in revised form 15 May 2003; accepted 1 July 2003
Abstract Deficits in early visual attention and perceptual organisation have frequently been shown to associate with both poor pre-morbid schizophrenia and those at a greater putative risk of psychosis. The nature of the deficit is unclear. The present study investigated the relationship between speed of visual marking and proneness to psychosis. 20 males and 20 females completed several tasks assessing speed of selection and deselection of visual objects. As predicted, negative schizotypy was associated with poorer marking in males, but socially desirable responding potentially confounded this result. In addition, impulsive non-conformity swas associated with poorer visual marking, more prominently in females. These results are discussed in relation to possible mechanisms by which psychosis-proneness and impulsivity may restrict the top–down influences operating on early visual attention. 2003 Elsevier Ltd. All rights reserved. Keywords: Psychosis-proneness; Impulsivity; Visual attention
1. Introduction A growing body of evidence suggests that various deficits in early visual attention are associated both with some forms of schizophrenia, and with a psychometrically greater risk of putative psychosis measured using questionnaires. With respect to schizophrenia, research findings are necessarily complicated by the exact nature of the task used, and by the sample. Studies of relatively late aspects of visual attention such as the formation of gestalt (Chey & Holzman, 1997) and global visual sensory store processing (Knight, Manoach, Elliott, & Hershenson, 2000) have *
Corresponding author. Tel.: +121-414-3836; fax: +121-414-4913. E-mail address: [email protected] (O.J. Mason).
0191-8869/$ - see front matter 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.paid.2003.07.015
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O.J. Mason et al. / Personality and Individual Differences 36 (2004) 1771–1779
generally found these to be intact. However, patients with a more chronic illness, greater cognitive disorganisation or poorer pre-morbid status (all of which indicate a higher genetic loading) have been shown to perform more poorly on perceptual grouping tasks (Silverstein, Kovacs, Corry, & Valone, 2000), and also fail to utilise top–down information in the form of added contextual cues (Silverstein et al., 1996a). The evidence supports the compromise of early attentional processes in those who have poorer pre-morbid function or go on to develop a more chronic illness; however, medication remains a potential confound to all studies in this area as it is precisely these patients who have received greater and longer treatment. Those studies that use non-clinical populations have measured differences in so-called schizotypal individual differences (Obiols, Garcia-Domingo, de Trincheria, & Domenech, 1993; Watson & Tipper, 1997; Rawlings & Goldberg, 2001). This research strategy has the potential advantage of both highlighting paradigms meriting further investigation in clinical conditions, as well as identifying markers of potential aetiological significance to psychosis, rather than deficits that are the consequence of it. Participants are also free of the potentially damaging effects of a psychiatric history including prolonged neuroleptic use. The current study uses this strategy to investigate individual differences in neuro-cognition that are of potential relevance to psychosis research. The majority of studies of cognitive processes in both patients and schizotypal individuals have used what might be termed multi-componential tasks that contain demands on stimulus selection, memory and sustained attention. Though of relevance to the argument that a deficit in ÔattentionÕ as a whole forms part of the diathesis to psychosis, tasks assessing latent inhibition, sustained attention and figure-ground discrimination are frequently less able to specify the cognitive neuropsychological nature of such a deficit. However, some researchers have suggested that at least part of the difficulty for schizophrenic patients is a problem of Ôdisregarding the irrelevant stimulusÕ (Braff, 1993; Schwartz & Evans, 1999). One concern has been to identify whether this is a limitation imposed by stimulus-driven (bottom–up) or knowledge-based (top–down) processes. Silverstein, Matteson, and Knight (1996b) found that schizophrenics could not use contextual cues to select auditory information but could use acoustic ones suggesting top–down limitations. Similar studies have extended this finding to visual patterns (Silverstein et al., 1996a; Silverstein, Bakshi, Chapman, & Nowlis, 1998). Both results suggest that top–down processes may be impaired in acute schizophrenia though the nature of this deficit is at present hard to specify. The present study attempts to clarify the nature of differences in top–down processing operating at an early stage of visual attention. One approach to the cognitive neuropsychology of visual attention that has received extensive attention has been termed visual marking (Watson & Humphreys, 1997). Watson and HumphreysÕ task aims to investigate how old objects are de-prioritised, so aiding efficient selection of new objects. Watson and Humphreys had participants search for a blue letter H among green Hs and blue As. There were three main conditions. In the standard conjunction search task, a target (when present) appeared among green H and blue A distractor items. In the standard singlefeature search condition, the blue H target had to be detected among blue letter A distractors. In the third, preview condition there was a temporal delay of 1000 ms between the onset of an initial subset of distractors (green Hs) and the onset of the remainder of the search items (blue A distractors and, on target-present trials, a blue H). Display sizes varied between 2 and 16 items. Interestingly, the slope of the search function for the preview condition was similar to that in the single-feature baseline and it was substantially less than that found in the color-form conjunction
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condition. The data show that, in the preview condition, the old green distractors had minimal impact on search. Converging results with the visual marking paradigm suggest that this process is a resource-limited process requiring attention control and not simply an automatic one (Watson & Humphreys, 2000; Olivers, Watson, & Humphreys, 1999). Proponents of visual marking argue that its active application makes sense in evolutionary terms, as marking would enable changes in complex environments (such as predator movement) to be efficiently monitored. Recent work has described the neuroanatomical basis of marking in both fMRI (Pollmann et al., 2003) and ERP studies (Jacobsen, Humphreys, Schroger, & Roeber, 2002). Activation of a frontal-parietal network is seen in all studies, with an initial locus in the central frontal areas, with greater activation on the left side in one study (Jacobsen et al., 2002). The time course of frontal activation (350–750 ms) is consistent with behavioural data on the stimulus onset asynchrony required for marking to occur and substantiates the Ôactive suppressionÕ of visual objects as an account of the phenomenon. Study of clinical phenomena associated with marking deficits has been limited, though one unpublished study has implicated poor marking associated with attention deficit disorder in adolescents (Humphreys, personal communication). Detailed analysis pointed to specific difficulty inhibiting an early (and inappropriate) response to the distracter set. We do not suggest that the attention deficit associated with psychosis-proneness would necessarily take this form. However, it is probable that there are several routes to deficits in visual marking associated with different neuropsychological impairments. The study aimed to delineate the nature of the attention deficit involved with psychosis-proneness further using the visual marking paradigm. A feature of contemporary measures of psychosis-proneness is their multi-dimensional nature (Raine, 1991; Mason, Claridge, & Jackson, 1995)––typically containing, at the least, measures of positive and negative schizotypy, as well as cognitive disorganisation. The measure used here also contains a fourth component called impulsive non-conformity that combines elements of psychoticism (Eysenck & Eysenck, 1976) with hypomania and borderline personality disorder. While this development to measurement has helped clarify the diversity of findings with proneness measures, it renders specific hypothesis testing challenging. Without prior findings it is difficult to specify which factor might relate to a particular deficit such as one of visual marking. However, several previous studies support both an attention deficit (Chen, Hsiao, & Lin, 1997) and poor somatosensory discrimination (Lenzenweger, 2000) in anhedonic individuals and those with chronic negative symptoms. In keeping with a range of findings of reduced parietal activity as a basis for negative symptoms (e.g. Tamminga, Buchannan, & Gold, 1998) we hypothesised negative schizotypy, in the form of introvertive anhedonia (Mason et al., 1995), to relate to visual marking ability as this has a parietal basis. However, it is difficult to rule out the other factors as some shared variance is frequently identified, and indeed a case can be made for an inhibitory deficit for any factor.
2. Method 2.1. Participants Forty undergraduate students (20 male and 20 female) at the University of Birmingham completed the measures of visual marking and psychosis-proneness. Ages ranged from 17 to 25
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(mean ¼ 19.0, s.d. ¼ 4.3). The participants were not informed of the purpose of the study. All reported having normal or corrected-to-normal vision and normal colour vision. 2.2. Design The design for the visual marking task was similar to that of Watson and Humphreys (1997) described in Section 1. There were three visual search conditions: single feature, conjunction and preview. Participants were presented with nine blocks of twenty-four trials: within blocks 1–3, 4–6 and 7–9, each condition appeared once in randomised order. Overall, participants were exposed to each condition three times. 2.3. Stimuli and apparatus All stimuli were presented on a sVGA monitor controlled by a PC/Mach64 VGA graphics card. The target was always present (light blue H) and the distracters were light green Hs and light blue As. In the conjunction and preview conditions, half the distracters were light green Hs and half were light blue As. In the preview condition there was a 1000 ms pause between the appearance of the first distracters (green Hs) and the presentation of the second set of distracters (blue As). The stimuli letters were 4 mm wide and 8 mm high. The search displays were generated by randomly positioning each item in the middle of cells making up an invisible 10 · 10 matrix. The overall matrix size was 137 mm wide by 135 mm high as used by Olivers et al. (1999). There were four new items in all trials making a total of eight items in preview and conjunction conditions. 2.4. Procedure Participants completed the visual marking task following instructions presented on the screen. The screen was viewed from a distance of 70 cm. On each trial a white fixation cross (1.3 mm · 1.3 mm) appeared in the centre of the screen for 1000 ms. Following this, the search display was presented and remained until the participant responded, or a time-out period of 5 s concluded. Responses were made by pressing the left-hand mouse key with the right index finger. Participants were required to press once as soon as they saw the target in the display. The display then disappeared and the outline of a matrix (5 · 5 circles) appeared on the screen against a black background––the circles represented possible locations for where the target had appeared. Participants were asked to move the mouse so that the screen arrow pointed to approximately where the target had appeared, and press once again. The first response was designed to measure reaction times, while the second provided a check of accuracy. Participants were asked to respond as quickly as possible, but to make as few errors as possible. If participants made an error during a trial, the trial was automatically re-shown at the end of that block, so that a full set of results was obtained. The task took 15 min to complete. After a short recovery period, participants completed the following personality scales. 2.5. Psychosis-proneness scales The following scales were drawn from the O-LIFE (Mason et al., 1995). Unusual experiences contains items describing perceptual aberrations, magical thinking and hallucinations. It is phenomenologically related to positive symptoms of psychosis. Cognitive
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disorganisation describes aspects of poor attention and concentration as well as poor decisionmaking and social anxiety. It can be seen to reflect thought disorder and other disorganised aspects of psychosis. Introvertive anhedonia describes a lack of enjoyment from social and physical sources of pleasure as well as avoidance of intimacy. It can be seen to reflect so-called Ônegative symptomsÕ, or alternatively the schizoid temperament. Impulsive non-conformity contains items describing impulsive, anti-social and eccentric forms of behaviour, often suggesting a lack of self-control. Psychometric evaluation of the O-LIFE has shown it to have good test–retest reliability (Burch, Steel, & Hemsley, 1998), internal consistency (r ¼ 0:8; Loughland & Williams, 1997) and factorial validity (Mason, 1995). An increasing literature has supported experimental findings across the range of scales with paradigms thought to reflect vulnerability to psychosis. In addition, the Lie scale was also included as a measure of socially desirable responding (Eysenck & Eysenck, 1975). 2.6. Indices of visual marking Mean reaction times were calculated for each participant in each condition from three blocks. Two indices of visual marking were calculated. The difference index was calculated by subtracting RTs in the preview condition from RTs in the conjunction condition. This difference is a measure of the superiority afforded by visual marking. A further index was calculated by dividing the difference by the single feature condition RT as a way of controlling for differences in overall speed.
3. Results 3.1. Descriptive statistics Results for both the visual marking task and personality measures are given in Table 1. By comparison to the norms provided for student populations, the males in the sample scored rather below those expected on the measure of unusual experiences and impulsive non-conformity. Results of t-tests of difference between males and females are also given in Table 1. On both unusual experiences and cognitive disorganisation, females scored more highly, in line with previous findings. Reaction times in the three experimental conditions are consistent with those previously found (Watson & Humphreys, 1997), and form the largest sample to date on this lengthy task. As expected, the single feature condition produces the lowest RTs, followed by the preview condition. In all individuals, the conjunction condition had the longest RTs, allowing a positive difference score to be calculated. No violations of normality were observed for any variable. There was a tendency for males to perform more quickly in all experimental conditions that reached significance in the conjunction condition. 3.2. Personality relationships with indices of visual marking Although two indices were calculated, results were identical for each; so only those with the difference index are reported. In practice this was due to a relatively narrow range of overall
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Table 1 Results on visual marking and psychosis-proneness measures Female Mean O-LIFE scales Unusual experiences Cognitive disorganisation Introvertive anhedonia Impulsive non-conformity Lie scale
Male s.d.
11.55 14.70 6.05 9.00 6.950
t (p-value)
Mean
s.d.
6.26 6.05 4.57 3.45
7.32 11.47 6.53 9.33
5.96 3.88 3.12 3.65
2.20 1.93 0.52 0.27
3.69
5.58
2.95
1.19 (ns)
Visual marking indices Single feature Conjunction Preview
681.4 985.4 787.0
146.3 183.3 151.4
611.7 864.4 712.2
160.2 185.6 167.0
Difference
198.3
89.4
156.7
66.7
(<0.05) (ns) (ns) (ns)
1.50 (ns) 2.22 (<0.05) 1.71 (ns) 1.66 (ns)
reaction times so that no need arose to control for differences in speed by using the simplest single feature task as a denominator. The relationships of visual marking with personality variables were examined by Pearson product-moment correlations, both for the group as a whole and separately for males and females (see Table 2). The difference index produced a trend in correlation with impulsive non-conformity (r ¼ 0:3, p ¼ 0:09) that was entirely due to the females in the sample (r ¼ 0:51, p < 0:01). The pattern of results appeared to be quite different for males: as predicted, introvertive anhedonia was significantly negatively correlated with the index. However, investigation of the male sample suggested a confounding influence of socially desirable responding (Lie scale). While the Lie scale was not significantly correlated with any other variables in females, in males it was significantly associated with impulsive non-conformity (r ¼ 0:59, p < 0:01). Although the small numbers do not permit the sample to be further subdivided, this was addressed by partial correlation, so removing the effects of social desirability statistically. When this is done, the difference index is reduced to a trend in relation to introvertive anhedonia in males (r ¼ 0:42, p ¼ 0:07), but a trend for a relationship appears with impulsive non-conformity (r ¼ 0:37, p ¼ 0:08).
Table 2 Correlations of psychosis-proneness scales with difference index
*
Scale
All
Male
Male (Lie partialled)
Female
Unusual experiences Cognitive disorganisation Introvertive anhedonia Impulsive non-conformity Lie
0.01 0.24 )0.20 )0.31 )0.02
0.24 0.08 )0.48 )0.02 )0.43
0.06 0.10 )0.42 )0.37 –
)0.19 0.24 )0.03 )0.51 0.08
p < 0:01. p < 0:1.
**
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4. Discussion The results supported the hypothesised relationship between psychosis-proneness and visual marking but were not entirely as predicted. Despite predicting associations with negative schizotypy in the form of introvertive anhedonia, reduced visual marking was more reliably associated with greater impulsive non-conformity. This finding was straightforward in the female sample but remains to be clarified in males. The hypothesised relationship with introvertive anhedonia did emerge in males but should be treated with caution because of the influence of social desirability. Potential relationships with schizotypy may be compromised by the non-representative nature (atypically low in some traits) of the male sample in the present study. We do not, therefore, regard the results in males as necessarily valid and further empirical work is clearly needed. However, gender differences are frequently seen in studies of psychosis-proneness and schizophrenia and may reflect different brain-behaviour relationships across gender (Gruzelier, 1994). The relationship of reduced visual marking with anhedonia is consistent with other results suggestive of poor attentional processing (Chen et al., 1997). Furthermore, although the evidence on visual marking is preliminary as discussed in the introduction, it is consistent with reductions in left hemisphere activation seen in a number of studies of negative schizotypy (Gruzelier & Richardson, 1994), and with the well-known hypo-frontality hypothesis. The relationship with impulsive non-conformity was somewhat less expected, though this is an aspect of psychosis-proneness that is not contained in many measures, and hence studies, in this field. However, the measureÕs clear similarity (and some content overlap) with EysenckÕs original Psychoticism scale (Eysenck & Eysenck, 1975) make it highly relevant to any study of psychosisproneness, and a finding related to poor attention is in no way at odds with his view. As Watson and Humphreys have demonstrated, visual marking involves attention-demanding top–down processes, probably in addition to automatic stimulus-property driven ones. Moreover, the magnitude of differences in visual marking (from around 68–370 ms) suggests that slower top– down processes are heavily involved. Recent empirical work (Olivers, Braithwaite, & Humphreys, in press) has clarified that there is both a search and an intercept effect––something not separated by the current paradigm using a single display size, and an admitted limitation of the study. Olivers et al. (in press) argue that the intercept effect is due to inhibiting a response to the preview, in contrast to using the preview to help guide search. It is currently unclear whether one, other or both effects are involved, though response inhibition is very clearly relevant to impulsivity. In this vein, the findings are consistent with a previously reported study of attention deficit disorder (Humphreys, personal communication), and would suggest that a greater degree of conscious control is required to suppress an early response to the distracters before the to-be-marked stimulus has occurred. Clearly further clarification is required: while the finding was clear in females, the relationship of impulsive non-conformity to differences in visual marking in males was uncertain. In part this might pertain to the rather low levels of schizotypal traits in the present study, and a wider sample of participants could help clarify the issue. The study also highlighted how socially desirable responding may be a potential confound in relationships between personality traits such as psychosis-proneness and experimental measures like visual marking. In particular, in males the relationship with introvertive anhedonia declined somewhat when socially desirable responding was controlled for, while a relationship with impulsive non-conformity appeared. As screening for the influence of social desirability has not
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hitherto been a feature of the majority of research in the field, this is strongly suggested as a desirable development.
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