Help-seeking pathways in early psychosis Introduction Understanding the help-seeking pathways of patients with a putative risk of developing psychosis helps improving development of specialised care services . This study aimed at obtaining information about : type of health professionals contacted by patients at putative risk for psychosis on their help-seeking pathways ; number of contacts ; type of symptoms leading to contacts with health professionals ; interval between initial contact and referral to a specialised outpatient service . Introduction In recent years , the aim of intervening in the early phases of psychosis has drawn great interest . Early intervention may shorten duration of untreated psychosis or even prevent onset of psychosis . Exact knowledge about the help-seeking pathways of patients is pivotal in order to provide early intervention and , thus , supply specialised and focussed health care . One study has investigated the patterns of referral in patients known to be at risk for developing a psychotic illness -LSB- 1 -RSB- . Further studies investigating these trajectories in first-episode patients -LSB- 2 -- 5 -RSB- were able to show the important role of GPs . GPs were reported to be commonly contacted by patients who later develop psychosis . In particular , GPs were often reported to be contacted early along the help-seeking pathways and were shown to commonly be the first contacted professional group -LSB- 3 -RSB- . It can thus be hypothesised that a considerable part of GPs are contacted by patients who may still be presenting more insidious features such as functional disability or social withdrawal , given that these insidious features have been found to be highly prevalent in the early course of psychosis -LSB- 6 -RSB- . It must therefore be expected that studies of help-seeking pathways which , in addition to first-episode patients , further include patients in presumed at-risk states for psychosis would be able to corroborate the importance of GPs as early contacted professional groups . Up to date , only one other such study has been reported on patients who are considered to be at-risk for psychosis , but who have not yet developed psychosis -LSB- 1 -RSB- . This study is the first to compare the help-seeking behaviour of at-risk patients , patients with first psychotic episodes and of patients neither meeting clinical at-risk nor first episode criteria , but who are concerned about their mental health and thus were assessed in a prodromal service . To the best of our knowledge , it is also the first study to assess symptoms in patients at risk for psychosis at their first presentation to a prodromal service . We expected GPs to be highly represented among the early help-seeking contacts of at-risk patients . Method Recruitment strategy In August 2002 , a specialised , low-threshold outpatient service for the assessment of patients considered at-risk for psychosis was established in a semi-urban catchment area of North Western Switzerland -LRB- population = 300.000 -RRB- . This `` prodromal clinic '' is part of the only general psychiatric outpatient clinic of the catchment area and is associated with a public psychiatric hospital . As is the case all over Switzerland , patients can refer themselves directly to any public or private psychiatric facility and do not require referral to mental health systems via gate-keeping GPs . Patients can also be referred by any other source such as GPs , school counsellors , paediatricians or social workers . Between August and December 2002 , the majority of GPs -LRB- n = 240 -RRB- , private psychiatrists and psychologists -LRB- n = 130 -RRB- of the catchment area were educated either individually or in small groups about the early warning signs of emerging psychosis and manifest psychotic features . Education strategies were based on the findings from a large , nation-wide survey among 1089 GPs -LSB- 7 -RSB- that showed that GPs often underidentified the insidious features of beginning psychosis , such as functional decline . In keeping with these findings , education strategies primarily focussed on the importance of the insidious features of beginning psychosis such as sustained functional decline and social withdrawal as important early warning signs . With the inclusion of the adolescent psychiatric service into our prodromal clinic in January 2004 , all private youth psychiatrists as well as paediatricians were equally enrolled in this campaign so as to ensure additional referrals of patients aged 14 -- 17 years , as symptom onset in this young age group has been associated with less favourable outcomes -LSB- 8 -RSB- . In our study , sensitised primary and secondary health care providers were encouraged to contact the outpatient clinic whenever one of their patients showed sustained decline in social functioning in a still relatively asymptomatic state ; if they showed attenuated or brief intermittent positive psychotic symptoms ; or if they suspected that `` something odd had been going on '' for some time in their patients . The research protocol was approved by the `` Ethikkommission beider Basel '' . It was designed to obtain data on help-seeking pathways and to collect longitudinal information about progression of symptoms and social as well as neuropsychological functioning , and was not a treatment trial . Patient sample As of January 1st 2003 , patients could be referred to our prodromal clinic . Consenting patients were included in the study . Each individual was fully informed about the research protocol . Written informed consent was obtained from all patients , and additionally from the parents if under 18 . Patients were considered ineligible for further assessment within the study if they presented a history of a past psychotic episode , traumatic brain injury , epilepsy or other known neurological disorder ; other significant medical conditions considered to affect cognitive performance and self-perception ; an IQ of below 70 ; or patients below the age of 18 in the first year and below the age of 14 years in the second year of the present study . Symptom ratings We assessed the entire range of potential symptoms from early prodrome to first psychotic episode using the following instruments : potential early prodromes were assessed using the Schizophrenia Prediction Instrument -- Adult Version -LRB- SPI-A -RRB- -LSB- 9 -RSB- , potential late prodromes using the Scale of Prodromal Symptoms -LRB- SOPS -RRB- with its companion interview manual -LRB- Structured Interview for Prodromal Symptoms , SIPS -RRB- -LSB- 10 , 11 -RSB- . For the assessment of potentially manifest psychosis , we used the Positive and Negative Syndrome Scale -LRB- PANSS ; 12 -RRB- . Ratings were performed by an experienced consultant research psychiatrist -LRB- A.S. -RRB- or by a trained masters-level psychologist -LRB- D.D. -RRB- . Interrater reliability was established by extensive training by one of the authors of the SPI-A and by repeated training sessions involving all raters . However , formal assessment of interrater reliability was not conducted . The SPI-A has been developed from a hierarchical cluster analysis of the BSABS -LSB- 13 -RSB- and includes those 10 basic symptoms for which a good positive predictive value for later schizophrenia has previously been reported -LSB- 14 , 15 -RSB- . These basic symptoms include : thought interferences ; thought perseveration ; thought pressure ; thought blockages ; disturbances of receptive language ; decreased ability to discriminate between ideas and perception , phantasy and true memory ; unstable ideas of reference ; derealisation ; visual and acoustic perception disturbances . The structure of the SIPS manual and the SOPS rating scale as well as its high validity and reliability have been reported elsewhere -LSB- 10 , 11 -RSB- . In summary , these authors classified patients with either attenuated positive psychotic symptoms , brief limited intermittent positive psychotic symptoms or with a combined functional decline and genetic high-risk as ultra high-risk -LRB- UHR -RRB- . Group assignment Depending on symptom severity , patients were assigned to one of the three following groups : -LRB- 1 -RRB- the First Episode -LRB- FE -RRB- group was constituted by patients scoring 6 on any of the five SOPS positive symptom items for more than 1 week , which is identical with a minimum score of 4 on any of the PANSS positive items for the same time period . -LRB- 2 -RRB- The at-risk -LRB- AR -RRB- group included : patients meeting severity , but not duration criteria of the FE group ; patients meeting scores of 3 -- 5 on any SOPS positive psychotic symptom item at least once a week over the past month ; patients with a first degree relative with any psychotic disorder and/or patient meeting DSM-IV Schizotypal Personality Disorder criteria and a 30 % or greater drop in the GAF -LSB- 16 -RSB- score during the last month compared to 12 months ago ; patients scoring a minimum of 3 on any of the 10 predictive basic symptoms according to the SPI-A . -LRB- 3 -RRB- Help-seeking patients who were referred to the prodromal clinic for risk assessment , but who did neither meet FE nor AR criteria , were assigned to the Patient Control -LRB- PCo -RRB- group . Assessment of help-seeking pathways and of symptoms at prior contacts After symptom assessment , patients were asked which other professional groups they had previously contacted for similar problems . Further , timing and number of contacts as well as type of symptom leading to each single prior contact were recorded and , whenever possible , corroborated with information from family members . These data were assessed using a semi-structured interview that was designed for this study . However , no information was collected whether referrals to mental health services were voluntary or involuntary . Analysis Data on patients who were enrolled between January 2003 and December 2004 were analysed using the computer package SPSS Version 11.04 . We compared number of contacts and professionals contacted along the help-seeking pathways between groups . Similarly , symptoms that patients had presented during their previous help-seeking contacts and the interval between initial contact and referral to our prodromal service were compared between groups . Continuous variables were compared with t-tests or ANOVA , categorical variables with χ2 tests or , if ranked , with Kruskal -- Wallis and Mann -- Whitney-U tests . An alpha level of 0.05 was considered significant . Results Sample characteristics Of the 104 patients included into this study , 28 were female and 76 male . The mean age was 23.2 years -LRB- SD : ± 5.43 ; range : 16 -- 38 -RRB- in the first year of the study , and 20.0 years -LRB- SD : ± 6.08 ; range : 14 -- 40 -RRB- in the second year . 28 patients met criteria for the FE group , 50 for the AR group , and 26 patients were assigned to the PCo group . A summary of the socio-demographic characteristics across these study groups is shown in Table 1 . Table 1Socio-demographic characteristicsFirst episodeAt-riskControlsTotalSignificance valuesNumber of patients285026104Mean age23 .42122.122 χ ² = 3.744 , df = 2 , P = 0.153 Gender m -LRB- % -RRB- 22 -LRB- 79 -RRB- 31 -LRB- 62 -RRB- 23 -LRB- 88 -RRB- 76 -LRB- 73 -RRB- χ ² = 6.676 , df = 2 , P = 0.036 f -LRB- % -RRB- 6 -LRB- 21 -RRB- 19 -LRB- 38 -RRB- 3 -LRB- 12 -RRB- 28 -LRB- 27 -RRB- Marriage status Unmarried -LRB- % -RRB- 26 -LRB- 93 -RRB- 45 -LRB- 90 -RRB- 25 -LRB- 96 -RRB- 96 -LRB- 92 -RRB- χ ² = 0.929 , df = 2 , P = 0.629 Children No children -LRB- % -RRB- 28 -LRB- 100 -RRB- 48 -LRB- 96 -RRB- 25 -LRB- 96 -RRB- 101 -LRB- 97 -RRB- χ ² = 1.140 , df = 2 , P = 0.566 Living situation Alone -LRB- % -RRB- 5 -LRB- 18 -RRB- 7 -LRB- 14 -RRB- 6 -LRB- 23 -RRB- 18 -LRB- 17 -RRB- χ ² = 8.412 , df = 4 , P = 0.078 With partner or friends -LRB- % -RRB- 5 -LRB- 18 -RRB- 5 -LRB- 10 -RRB- 8 -LRB- 31 -RRB- 18 -LRB- 17 -RRB- With parents or relatives -LRB- % -RRB- 18 -LRB- 64 -RRB- 36 -LRB- 72 -RRB- 10 -LRB- 39 -RRB- 64 -LRB- 62 -RRB- City size > 200,000 -LRB- % -RRB- 5 -LRB- 18 -RRB- 5 -LRB- 10 -RRB- 4 -LRB- 15 -RRB- 14 -LRB- 14 -RRB- χ ² = 3.337 , df = 6 , P = 0.766 10,000 -- 200,000 -LRB- % -RRB- 7 -LRB- 25 -RRB- 12 -LRB- 24 -RRB- 6 -LRB- 23 -RRB- 25 -LRB- 24 -RRB- < 10,000 -LRB- % -RRB- 16 -LRB- 57 -RRB- 33 -LRB- 66 -RRB- 16 -LRB- 62 -RRB- 59 -LRB- 62 -RRB- School education None completed -LRB- % -RRB- 1 -LRB- 4 -RRB- 1 -LRB- 2 -RRB- 2 -LRB- 8 -RRB- 4 -LRB- 4 -RRB- χ ² = 4.688 , df = 6 , P = 0.584 Obligatory school -LRB- % -RRB- 19 -LRB- 68 -RRB- 36 -LRB- 72 -RRB- 18 -LRB- 69 -RRB- 73 -LRB- 70 -RRB- Maturity -LRB- % -RRB- 5 -LRB- 18 -RRB- 4 -LRB- 8 -RRB- 4 -LRB- 15 -RRB- 13 -LRB- 13 -RRB- Still in education -LRB- % -RRB- 3 -LRB- 11 -RRB- 9 -LRB- 18 -RRB- 2 -LRB- 8 -RRB- 14 -LRB- 13 -RRB- Professional training None -LRB- % -RRB- 9 -LRB- 32 -RRB- 22 -LRB- 44 -RRB- 8 -LRB- 31 -RRB- 39 -LRB- 38 -RRB- χ ² = 10.429 , df = 6 , P = 0.108 Apprenticeship -LRB- % -RRB- 12 -LRB- 42 -RRB- 18 -LRB- 36 -RRB- 12 -LRB- 46 -RRB- 42 -LRB- 40 -RRB- Academic education -LRB- % -RRB- 5 -LRB- 18 -RRB- 1 -LRB- 2 -RRB- 1 -LRB- 4 -RRB- 7 -LRB- 7 -RRB- Still in training -LRB- % -RRB- 2 -LRB- 7 -RRB- 9 -LRB- 18 -RRB- 5 -LRB- 19 -RRB- 16 -LRB- 15 -RRB- Work situation No occupation -LRB- % -RRB- 12 -LRB- 43 -RRB- 19 -LRB- 38 -RRB- 10 -LRB- 39 -RRB- 41 -LRB- 39 -RRB- χ ² = 4.097 , df = 6 , P = 0.664 At work -LRB- % -RRB- 10 -LRB- 36 -RRB- 11 -LRB- 22 -RRB- 6 -LRB- 22 -RRB- 27 -LRB- 26 -RRB- In training -LRB- % -RRB- 6 -LRB- 21 -RRB- 20 -LRB- 40 -RRB- 10 -LRB- 39 -RRB- 36 -LRB- 35 -RRB- Number of contacts and professionals contacted The mean number of contacts over all three patient groups was 2.38 -LRB- SD : ± 1.42 ; median : 3.0 ; range : 1 -- 8 -RRB- with no significant between-group differences -LRB- χ2 = 208.375 , df = 2 , P = 0.605 -RRB- . The overall patient sample reported a total of 247 contacts prior to their referral to our prodromal clinic . Table 2 shows the type of professional groups contacted by the patients across the three study groups along their help-seeking trajectories . FE patients more often presented themselves to mental health professionals -LRB- psychiatrists , psychologists as well as psychiatric out - and in-patient services -RRB- than AR and PCo patients -LRB- 71.2 % vs. 57.6 % vs. 53.5 % of contacts -RRB- ; however , this comparison did not reach significance -LRB- χ2 = 4.724 , df = 2 , P = 0.094 -RRB- . When comparing FE patients with the combined non-psychotic AR and PCo patients , FE patients significantly more often presented themselves to mental health professionals -LRB- χ2 = 4.461 , df = 1 , P = 0.024 -RRB- . Furthermore , when comparing the numbers of contacts with mental health professionals -LRB- 149/247 = 60.3 % -RRB- with those to non-mental health professionals -LRB- 98/247 = 39.7 % -RRB- , FE patients more often contacted in-patient services , whereas PCo and AR patients more often attended GPs and `` other '' professionals such as alternative medical practitioners , non-medical counselling services and non-specified professionals -LRB- χ2 = 20.189 , df = 8 , P = 0.010 -RRB- . Of the overall sample , 51.0 % -LRB- 53/104 -RRB- contacted a GP at some point in time , whereas 83.7 % had at least once visited a mental health professional . Table 2Distribution of professionals contactedFEARPCoTotal -LRB- n -RRB- % of total -LRB- 66 -RRB- 26.7 -LRB- 125 -RRB- 50.6 -LRB- 56 -RRB- 22.7 -LRB- 247 -RRB- 100General practitioners21 .2 % -LRB- 14 -RRB- 21.6 % -LRB- 27 -RRB- 37.5 % -LRB- 21 -RRB- 25.1 % -LRB- 62 -RRB- Private Psychiatrists/Psychologists21 .2 % -LRB- 14 -RRB- 24.8 % -LRB- 31 -RRB- 21.4 % -LRB- 12 -RRB- 23.1 % -LRB- 57 -RRB- Psychiatric out-patient services30 .3 % -LRB- 20 -RRB- 25.6 % -LRB- 32 -RRB- 16.1 % -LRB- 9 -RRB- 24.7 % -LRB- 61 -RRB- Psychiatric in-patient services19 .7 % -LRB- 13 -RRB- 7.2 % -LRB- 9 -RRB- 16.1 % -LRB- 9 -RRB- 12.6 % -LRB- 31 -RRB- Other professionals7 .6 % -LRB- 5 -RRB- 20.8 % -LRB- 26 -RRB- 8.9 % -LRB- 5 -RRB- 14.6 % -LRB- 36 -RRB- Percentages -LRB- and absolute numbers -RRB- of contacts made with professional groups at any stage of the help-seeking pathway However , as shown in Fig. 1 , there was a trend for progression from non-psychiatric towards psychiatric services . Contacts with GPs were often at an earlier stage on the help-seeking pathways . Moreover , GPs were the most often first-contacted professional groups , whereas psychiatric in-patient services were most commonly the last contacted professional group -LRB- χ2 = 15.816 , df = 4 , P = 0.003 -RRB- . However , differences among study groups did not reach significance -LRB- first contacts : χ2 = 13.102 , df = 8 , P = 0.108 ; last contacts : χ2 = 9.699 , df = 8 , P = 0.287 -RRB- . Fig. 1Progression to specialized services . Distribution of first -LRB- n = 104 -RRB- and last contacts -LRB- n = 104 -RRB- in percent made to different helper groups . Contacts representing the only help-seeking attempt by a subject appear in both first and last contacts Symptoms at prior presentations The complete set of signs and symptoms which led patients or their relatives to seek help at each of the recorded contacts was obtained from 100 of the total patient sample -LRB- 96.2 % -RRB- . The frequencies of the most commonly presented symptoms are shown in Table 3 . In the AR and PCo groups , the trias depression , social decline and social withdrawal were presented most frequently . In the FE group , unusual thought content was the most frequent symptom , followed by the above-mentioned triad . Table 3Frequency of presented symptomsFEARPCoTotalNumber of contacts6612556247Positive symptoms Ideas of reference -LRB- % -RRB- 15 -LRB- 23.1 -RRB- 2 -LRB- < 5.0 -RRB- 1 -LRB- < 5.0 -RRB- 18 -LRB- 7.7 -RRB- Unusual contents of thought -LRB- % -RRB- 36 -LRB- 55.4 -RRB- 18 -LRB- 14.8 -RRB- 1 -LRB- < 5.0 -RRB- 55 -LRB- 23.5 -RRB- Hallucinations -LRB- % -RRB- 13 -LRB- 20.0 -RRB- 11 -LRB- 9.0 -RRB- 2 -LRB- < 5.0 -RRB- 26 -LRB- 11.1 -RRB- Perceptual disturbances -LRB- % -RRB- 5 -LRB- 7.7 -RRB- 21 -LRB- 17.2 -RRB- 026 -LRB- 11.1 -RRB- Alienation or derealisation -LRB- % -RRB- 16 -LRB- 24.6 -RRB- 29 -LRB- 23.8 -RRB- 045 -LRB- 19.2 -RRB- Negative symptoms Deterioration of social functioning -LRB- % -RRB- 32 -LRB- 49.2 -RRB- 54 -LRB- 44.3 -RRB- 16 -LRB- 34.0 -RRB- 102 -LRB- 43.6 -RRB- Social withdrawal -LRB- % -RRB- 32 -LRB- 49.2 -RRB- 42 -LRB- 34.4 -RRB- 14 -LRB- 29.8 -RRB- 88 -LRB- 37.6 -RRB- Avolition -LRB- % -RRB- 9 -LRB- 13.8 -RRB- 26 -LRB- 21.3 -RRB- 12 -LRB- 25.5 -RRB- 47 -LRB- 20.1 -RRB- Cognitive symptoms Impaired concentration -LRB- % -RRB- 13 -LRB- 20.0 -RRB- 29 -LRB- 23.8 -RRB- 1 -LRB- < 5.0 -RRB- 43 -LRB- 18.4 -RRB- Impaired attention -LRB- % -RRB- 7 -LRB- 10.8 -RRB- 12 -LRB- 9.8 -RRB- 1 -LRB- < 5.0 -RRB- 20 -LRB- 8.5 -RRB- Impaired memory -LRB- % -RRB- 10 -LRB- 15.4 -RRB- 5 -LRB- < 5 -RRB- 2 -LRB- < 5.0 -RRB- 17 -LRB- 7.3 -RRB- Formal thought disorders -LRB- % -RRB- 17 -LRB- 26.2 -RRB- 25 -LRB- 20.5 -RRB- 042 -LRB- 17.9 -RRB- Other symptoms Depression -LRB- % -RRB- 24 -LRB- 36.9 -RRB- 74 -LRB- 60.7 -RRB- 38 -LRB- 80.9 -RRB- 136 -LRB- 58.1 -RRB- Anxiety -LRB- % -RRB- 14 -LRB- 21.5 -RRB- 27 -LRB- 22.1 -RRB- 9 -LRB- 19.1 -RRB- 50 -LRB- 21.4 -RRB- Lack of impulse-control -LRB- % -RRB- 2 -LRB- < 5.0 -RRB- 14 -LRB- < 5.0 -RRB- 11 -LRB- 23.4 -RRB- 27 -LRB- 11.5 -RRB- Absolute numbers -LRB- percentages -RRB- of presented symptoms . Percentage values do not add to 100 % due to multiple symptoms recorded for most contacts FE patients had presented at least one positive symptom in 80.3 % of their prior contacts , AR patients in 56.6 % and PCo patients in 5.9 % of their prior contacts -LRB- χ2 = 65.680 , df = 2 , P < 0.001 -RRB- . Similarly , when comparing numbers of patients rather than numbers of contacts , 89 % FE , 65 % AR and 8 % PCo patients had reported positive symptoms at any stage along their help-seeking pathway -LRB- χ2 = 35.483 , df = 2 , P < 0.001 -RRB- . Of patients presenting positive symptoms along their help-seeking pathways , 81.2 % already did so during their first contact . Positive symptoms were significantly more often reported in first help-seeking contacts with psychiatric out-patient -LRB- 63.6 % -RRB- and in-patient -LRB- 100 % -RRB- services as compared to GPs -LRB- 37.1 % -RRB- and private psychiatrists/psychologists -LRB- 31.8 % -RRB- -LRB- χ2 = 13.425 , df = 4 , P = 0.009 -RRB- . Table 4 shows the relationship between positive and non-positive symptoms and the professional groups to whom they were presented . Positive symptoms were significantly more often reported in contacts with both psychiatric out - and in-patient services -LRB- 67.2 % , 70.0 % -RRB- as compared to GPs , who were contacted for positive symptoms only in 37.3 % recorded contacts . Consequently , GPs were contacted with more unspecific symptoms -LRB- 62.7 % -RRB- such as depression and negative symptoms -LRB- χ2 = 18.046 , df = 4 , P = 0.01 -RRB- . Table 4Positive vs. non-positive symptoms presented to professional groupsGeneral practitionersPsychiatrists psychologistsOut-patient servicesIn-patient servicesOther xprofessionalsTotalNumber of contacts5955613034239Contacts made with positive symptoms37 .3 % -LRB- 22 -RRB- 40 % -LRB- 22 -RRB- 67.2 % -LRB- 41 -RRB- 70 % -LRB- 21 -RRB- 55.9 % -LRB- 19 -RRB- -LRB- 125 -RRB- Contacts made with non-positive symptoms62 .7 % -LRB- 37 -RRB- 60 % -LRB- 33 -RRB- 32.8 % -LRB- 20 -RRB- 30.0 % -LRB- 9 -RRB- 44.1 % -LRB- 15 -RRB- -LRB- 114 -RRB- Percentages -LRB- absolute numbers -RRB- of symptoms presented to professional groups . Percentage values do not add to 100 % due to multiple symptoms recorded for most contactsPositive symptoms included items according to Table 3 , non-positive symptoms included items according to `` negative '' , `` cognitive '' or `` other '' symptoms in Table 3 Duration from initial contact to referral The median interval from initial contact to time of referral to our prodromal clinic was 36 weeks -LRB- range : 1 day to 7.6 years ; mean : 124.0 weeks ; ± SD 217.1 -RRB- . About a third -LRB- 33.3 % -RRB- of the patients whose initial contact was over 18 months before referral to the prodromal clinic accounted for the relatively long mean help-seeking duration . Two-thirds -LRB- 66.6 % -RRB- , however , were referred within 18 months , with one-third -LRB- 35.4 % -RRB- being referred within 2 months . The median help-seeking duration of the FE group -LRB- 12.5 weeks -RRB- was shorter than for the AR -LRB- 42.5 weeks -RRB- and PCo groups -LRB- 46.5 weeks -RRB- , however , between-group comparisons dropped just below level of significance -LRB- z = − 1.879 , P = 0.06 -RRB- . More significantly , patients presenting with positive symptoms at some stage along their help-seeking trajectories -LRB- n = 56 -RRB- showed shorter pathway durations -LRB- median = 24.5 weeks -RRB- than patients presenting only with negative , affective or `` unspecific '' symptoms , i.e. patients never presenting positive symptoms -LRB- n = 44 ; median = 46.0 weeks -RRB- -LRB- z = − 2.072 , P = 0.038 -RRB- . We further calculated the median intervals from any of the prior contacts to the time of referral and compared these `` delays to referral '' for the different professional groups that were contacted . Median `` referral delay '' across all three-study groups was 28 weeks with no between-group differences -LRB- z = − 1.260 , P = 0.208 -RRB- . Median `` delays '' were 15 weeks for contacts with GPs , 68.5 weeks for private psychiatrists and psychologists , each 13.0 weeks for psychiatric in - and out-patient services , and 52.2 weeks for contacts made to `` others '' -LRB- z = − 3.554 , P < 0.001 -RRB- . For 165 of the 247 recorded contacts , we were able to obtain information on whether a continuous treatment of three or more consecutive sessions was provided . The significantly longer `` delays to referral '' following contacts with private psychiatrists and psychologists was associated with the finding that in 58 % of all contacts made with these groups , three or more sessions were administered . In comparison , in the vast majority of the cases -LRB- 83.7 % -RRB- contacts with GPs were single consultations . Discussion To the best of our knowledge , this is the first study to investigate the help-seeking pathways of a patient cohort , which was referred to a prodromal clinic for a suspected at-risk state for psychosis . We were able to confirm the important role of GPs along the help-seeking pathways of patients with emerging psychosis . Furthermore , GPs were contacted in particular by those patients who presented insidious features . It was these patients that showed the longest delays in referral to our specialised outpatient service . The importance of GPs along the early pathways This study was able to confirm recent reports from Australia -LSB- 1 -RSB- and from Germany -LSB- 17 , 18 -RSB- that a substantial number of contacts made along the help-seeking pathways were with mental health care professionals . As the gatekeeping model applies for Australia , but not for Germany or Switzerland , mental health care professionals seem to play an important role independent of a particular health system . At the same time , our study also confirms earlier reports -LSB- 2 -- 5 -RSB- about the pivotal role of GPs in the early pathways to care of help-seeking individuals that were referred to our prodromal clinic for an assessment of a potential psychotic at-risk state . While they were solicited in half of all contacts , GPs even constituted the most frequently first-contacted professional group -LRB- 34.6 % -RRB- . It is noteworthy that in Switzerland patients can refer themselves to GPs without a `` gate-keeping '' GP . It can be thus assumed that in health systems with `` gate-keeping '' GPs -LSB- 19 -RSB- , the present results may be even more representative . The challenge of detecting the insidious symptoms In addition , our results revealed that patients in less symptomatic states more commonly seek help with their GPs . Patients with manifest psychotic symptoms , however , more often contacted specialists . These results are paralleled by the finding that a shift from contacts made with primary carers to contacts with more specialised professional groups is taking place along the pathways -LRB- as shown in Fig. 1 -RRB- . Similar findings were reported by Lincoln et al. -LSB- 3 -RSB- . We assume that this process may also be an expression of the symptom progression along the course of early psychosis -LSB- 20 , 21 -RSB- . As we thus had expected , GPs are faced with the difficult task to detect potential at-risk states in patients that do not yet present psychotic , but the unspecific insidious features . This finding is of particular relevance as a recent comprehensive survey among 1089 Swiss GPs was able to show that GPs commonly under-identified the insidious features of emerging psychosis -LSB- 7 -RSB- . Preliminary results of an international replication study -LRB- IGPS -RRB- of the Swiss survey across 10 countries were able to confirm these findings -LSB- 22 -RSB- . Although features such as functional disability or social isolation may not necessarily lead to overt psychosis and may either be expression of another psychiatrically relevant process or remit after time , it is the detection of the earliest signs and symptoms of emerging psychosis that has become the aim of preventive efforts . Similarly , depression has been shown to be highly prevalent in emerging psychosis -LSB- 6 -RSB- . While this triad -- functional disability , social isolation and depression -- was found to be highly prevalent across all groups in the present study , it is also a characteristic of the deficit syndrome of schizophrenia -LSB- 23 -RSB- . If such symptoms are true-positive precursors of later psychosis , the non-detection of such patients contributes to a substantial delay on their way to specialised services and adequate treatment , which in turn has been shown to negatively affect the outcome of patients with first-episode psychosis -LSB- 24 -RSB- . Accordingly , our study confirmed earlier reports that patients with more insidious features showed longer pathway durations than patients with predominant positive symptoms -LSB- 25 -RSB- . Deficit syndrome patients , however , may show lower adherence to treatment and are per se characterised by worse outcomes -LSB- 23 -RSB- . Delays in referral Interestingly , when compared to specialists and other professional groups , GPs referred patients more rapidly to other professional groups once they were contacted . In contrast , more contacts per patient were found with private psychiatrists and psychologists before final referral to the prodromal clinic was established . Partially , this finding may be explained by our large and repetitious sensitisation of GPs about the insidious features of early psychosis . However , some of the sampled patients had contacted a GP before the sensitisation had taken place , suggesting that GPs tend to refer such patients more rapidly . This would be in line with the findings from both the Swiss survey -LSB- 7 -RSB- and its international replication study -LSB- 22 -RSB- , in which GPs indicated that they wished to rapidly refer patients in whom they suspected a beginning psychosis to specialised outpatient services . Given their degree of specialty , private psychiatrists and psychologists , in contrast , seem not to engage into rapid referral of these patients . Given the considerable potential for recall bias , our study did not assess type of treatment that was provided to patients at each of their contacts . Thus , no conclusions can be drawn about the adequacy of applied treatment strategies . It may be the psychiatrists and psychologists that are seeing the more symptomatic and `` difficult-to-treat '' patients who require a stable and continuous treatment setting . However , all patients included into this study were finally referred to our prodromal clinic , which may have either taken place for diagnostic assessment or for optimising treatment . It may thus be suggested that referrals of patients could have ideally been initiated already at an earlier stage along their help-seeking pathways . Interestingly , in two German studies on the pathways to care of patients with first-episode psychosis , contacts with private psychiatrists and psychologist were associated with longer duration of untreated psychosis as compared to GPs and general casualty services -LSB- 17 , 18 -RSB- . Taken together , these findings suggest that education may not only need to include primary carers such as GPs , but also other professional groups as well as secondary carers such as private psychiatrists and psychologists . Number of contacts and duration of help-seeking pathways Finally , the comparatively low mean number of contacts -LRB- 2.38 -RRB- on the pathways to care over all patient groups may express the effect of the large sensitisation of professional groups that was conducted when our prodromal clinic was established . This finding is identical with the Phillips et al. study -LSB- 1 -RSB- who reported a mean number of contacts of 2.36 in their at-risk sample . Additionally , the median duration from initial contact to referral to our prodromal service was very similar to the one reported by Phillips et al. -LSB- 1 -RSB- -LRB- 42.5 vs. 41.4 weeks -RRB- . In those studies assessing help-seeking pathways of first-episode cohorts , only one other study reported lower mean contacts -LRB- 1.7 ; range 1 -- 4 -RRB- and also was conducted as part of an early psychosis service -LSB- 5 -RSB- . In comparison , number of contacts of patient samples not treated in specialised services were reported to be higher . A mean number of contact of 4.9 was reported by Johnstone et al. -LSB- 2 -RSB- , a finding which was identically reported in a study that included patients treated before and after the establishment of an early psychosis service -LSB- 3 -RSB- . These findings point to the importance of specialised early psychosis services . Weaknesses of this paper Finally , a few weaknesses of this survey should be acknowledged . First , this study , like any retrospective research , is limited by an inherent potential for recall bias . Given the considerable length of pathway duration in the case of some patients , information on the exact number and on timing of contacts may be subject to errors . Ideally , all contacted professional groups would need to be contacted and interviewed in order to validate the information obtained by patients and their relatives . Second , pathways were studied on a patient sample , which was mainly constituted by subjects without manifest psychosis . Contacted professional groups may therefore not have been alarmed to refer their patients , and referral to our prodromal clinic may have only occurred in order to exclude an at-risk state for psychosis once the prodromal clinic was established . It can , however , be suggested that referrals would only take place if there is particular need for further assessment . Moreover , referrals may also have been initiated by patients themselves , although we did not control for that aspect in our study . Third , we can not exclude that pathways may differ in patients that are never referred to our prodromal clinic . It may well be possible that an unknown number of patients in presumed at-risk states are treated by private specialists and undergo complete remission . It may therefore be a per se selection of more impaired patients that will be referred to a prodromal clinic . Although the at-risk criteria applied in the current study are now well-established in the early psychosis research community -LSB- 26 -RSB- , it may well be possible that not all true at-risk patients meet these criteria . Thus , our study may have only captured a fraction of the individuals developing psychosis -LSB- 27 -RSB- . Fourth , we did not control for patient-related factors that may in a large part contribute to referral delays . These factors may include lack of insight , poor social adjustment , paranoid thoughts or avolition . Finally , the training and role of GPs in the health care system may vary across countries ; thus , not all of the findings of our study may be generalisable to other settings . However , our findings emerge from a health system where specialists may be contacted without the referral of the `` gate-keeping '' GPs . Thus , in health systems with gate-keeping models our findings that GPs are more commonly contacted by individuals with insidious features may warrant appropriate education efforts even stronger . Conclusions Our study confirms earlier reports of the GPs ' important role on the help-seeking pathways of psychotic patients . Furthermore , our study revealed that GPs are often contacted by patients with suspected at-risk states for psychosis early on their pathways to care . The insidious nature of the symptoms presented by these patients in the early stages of their pathways imposes an important challenge for GPs , as insidious features of early psychotic stages are difficult to detect . Our results thus support the need for appropriate education of GPs on these insidious features and for rapidly accessible specialised outpatient services . In a few countries , such specialized outpatient services have been established in recent years -LSB- 28 -RSB- . For example , in England , under the National Health Service Plan , 50 early intervention teams have been established at a cost of # 70 million -LSB- 29 -RSB- . It can thus be expected that help-seeking pathways of patients in early phases of psychosis may be reduced , thus maybe improving the overall outcome of patients .

O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O

early psychosis
prodrome
first episode
schizophrenia


Contrast

discrimination

Second

responses

reveal

the

relationship

between

the

mean

and

variance

of

visual

signals

To

explain

the

relationship

between

first

and

second-response

accuracies

in

a

detection

experiment

Swets

Tanner

and

Birdsall

-LSB-

Swets

J.

Tanner

W.

P.

Jr.

Birdsall

T.

G.

-LRB-

-RRB-

Decision

processes

in

perception

Psychological

Review

-RSB-

proposed

that

the

variance

of

visual

signals

increased

with

their

means

However

both

a

low

threshold

and

intrinsic

uncertainty

produce

similar

relationships

I

measured

the

relationship

between

first

and

second-response

accuracies

for

suprathreshold

contrast

discrimination

which

is

thought

to

be

unaffected

by

sensory

thresholds

and

intrinsic

uncertainty

The

results

are

consistent

with

a

slowly

increasing

variance

Introduction

First

applied

to

psychophysical

data

by

Tanner

and

Swets

-LRB-

-RRB-

signal-detection

theory

-LRB-

SDT

-RRB-

posits

that

all

stimuli

elicit

some

sensation

However

due

to

noise

sensations

experienced

in

the

absence

of

stimulus

can

sometimes

be

more

intense

than

sensations

actually

elicited

by

a

stimulus

Crucial

evidence

for

these

faint

hallucinations

comes

from

Swets

Tanner

and

Birdsall

's

-LRB-

-RRB-

two-response

four-alternative

forced-choice

-LRB-

-RRB-

detection

experiment

in

which

observers

reported

both

their

first

and

second

choices

for

the

temporal

position

of

a

visual

target

SDT

predicts

that

second-guessing

should

be

better

than

chance

and

this

is

what

Swets

et

al.

found

Signal-detection

theory

According

to

SDT

-LRB-

Green

Swets

-RRB-

each

stimulus

X

gives

rise

to

a

Gaussian

probability-density

function

-LRB-

PDF

-RRB-

of

sensory

intensity

x

In

its

simplest

form

all

PDF

's

have

the

same

standard

deviation

i.e.

σX

σ

X.

Increasing

variance

Simple

SDT

proved

incapable

of

explaining

Swets

et

al.

's

-LRB-

-RRB-

detection

experiment

Instead

they

proposed

that

sensation

variance

increased

with

sensation

mean

Increases

in

the

sigma-to-mean

ratio

r

dσX/dμX

produce

decreases

in

both

first

and

second-response

accuracies

but

the

second-response

accuracies

to

decrease

faster

Swets

et

al.

tried

several

values

for

this

ratio

and

obtained

as

good

fit

to

their

data

when

r

Intrinsic

uncertainty

Elsewhere

-LRB-

Solomon

-RRB-

Swets

et

al.

's

-LRB-

-RRB-

data

have

been

successfully

fit

with

an

alternative

model

incorporating

intrinsic

uncertainty

Intrinsic-uncertainty

models

posit

that

perceived

intensity

depends

on

the

maximum

activity

in

several

independent

sensory

mechanisms

only

one

of

which

is

actually

sensitive

to

the

stimulus

Given

a

sufficient

number

M

of

these

mechanisms

the

variance

of

their

maximum

activity

will

decrease

as

the

intensity

of

the

stimulus

decreases

-LRB-

see

Pelli

for

a

graphical

demonstration

of

this

-RRB-

Thus

to

some

degree

intrinsic

uncertainty

mimics

Swets

et

al.

's

proposal

of

increasing

variance

With

suprathreshold

stimuli

the

maximum

activity

always

occurs

in

the

appropriately

tuned

mechanism

and

the

others

have

no

influence

on

perception

Low-threshold

theory

At

odds

with

SDT

is

the

idea

of

a

sensory

threshold

which

weak

stimuli

must

exceed

to

be

detected

In

a

detection

task

stimuli

that

do

not

exceed

the

threshold

can

be

selected

only

when

no

other

stimulus

exceeds

it

and

the

observer

is

forced

to

make

a

choice

Swets

et

al.

-LRB-

-RRB-

developed

this

idea

into

a

low-threshold

hybrid

of

signal-detection

and

threshold

theories

Unlike

other

models

with

this

name

Swets

et

al.

claimed

theirs

could

fit

the

results

Elsewhere

-LRB-

Solomon

-RRB-

I

have

corroborated

this

claim

and

shown

that

the

fit

is

not

quite

as

good

as

those

produced

by

models

including

either

intrinsic

uncertainty

or

increasing

variance

This

study

Neither

intrinsic

uncertainty

-LRB-

Pelli

Tanner

-RRB-

nor

Swets

et

al.

's

-LRB-

-RRB-

low-threshold

theory

requires

sensation

variance

to

increase

with

sensation

mean

These

theories

are

somewhat

special

because

they

are

thought

to

affect

the

visibility

of

only

very

faint

stimuli

Increasing

variance

on

the

other

hand

has

implications

for

suprathreshold

contrast

discrimination

For

this

reason

I

decided

to

conduct

a

contrast-discrimination

experiment

The

goal

was

to

obtain

an

estimate

of

the

sigma-to-mean

ratio

which

would

not

be

contaminated

by

intrinsic

uncertainty

or

a

low

threshold

Methods

There

were

five

observers

the

author

-LRB-

JAS

-RRB-

another

psychophysicist

who

understood

the

purposes

of

the

experiment

-LRB-

MJM

-RRB-

two

experienced

psychophysical

observers

who

were

naïve

to

the

purposes

of

this

experiment

-LRB-

FV

and

MT

-RRB-

and

one

further

observer

who

had

no

previous

laboratory

experience

-LRB-

NN

-RRB-

As

described

below

NN

produced

a

very

high

proportion

of

finger

errors

This

suggested

to

us

a

general

unreliability

and

no

further

analyses

were

performed

on

his

data

The

Psychophysica

-LRB-

Watson

Solomon

-RRB-

software

used

in

these

experiments

is

available

at

The

display

-LRB-

a

Sony

GDM

CRT

-RRB-

was

viewed

in

a

dark

room

from

m.

Luminances

of

vertically

adjacent

pixels

were

effectively

independent

and

could

obtain

any

value

between

and

Stimuli

were

horizontal

cosine-phase

Gabor

patterns

whose

wavelength

and

spatial

spread

were

λ

and

σ

respectively

Stimuli

were

flashed

simultaneously

in

four

positions

each

marked

by

four

dark

spots

The

centers

of

these

positions

formed

a

square

centered

on

fixation

-LRB-

see

Fig.

-RRB-

On

each

trial

three

stimuli

appeared

with

a

pedestal

contrast

which

varied

between

blocks

of

trials

each

The

contrast

of

the

fourth

stimulus

was

somewhat

greater

After

each

stimulus

exposure

observers

gave

two

responses

The

first

response

indicated

which

of

the

four

positions

the

observer

thought

most

likely

to

have

contained

the

high-contrast

target

The

second

responses

from

JAS

and

MJM

indicated

their

second

choices

for

the

target

position

Following

their

second

responses

JAS

and

MJM

received

auditory

feedback

indicating

which

if

either

of

their

responses

was

correct

The

naïve

observers

were

not

told

that

three

of

the

four

stimuli

would

have

the

same

contrast

They

were

instructed

merely

to

indicate

their

choices

for

the

positions

containing

the

two

highest

contrasts

in

order

This

encouraged

them

to

fully

consider

their

second

responses

even

when

they

felt

confident

about

their

first

The

naïve

observers

received

no

feedback

Although

I

was

primarily

concerned

with

suprathreshold

contrast

discrimination

I

was

also

eager

to

replicate

Swets

et

al.

's

-LRB-

-RRB-

findings

at

detection

threshold

Since

I

was

therefore

committed

to

measuring

both

the

left

and

right

ends

of

the

threshold-vs

contrast

function

-LRB-

Nachmias

Sainsbury

Fig.

-RRB-

I

decided

to

devote

a

few

extra

trials

to

get

the

middle

as

well

-LRB-

Note

due

to

limited

availability

FV

performed

only

the

critical

conditions

i.e.

those

with

supra-threshold

pedestals

-RRB-

Table

shows

the

number

of

trials

each

observer

performed

with

each

pedestal

contrast

In

it

and

in

the

discussion

below

I

use

the

conventional

decibel

scale

of

contrast

energy

if

m

is

the

maximum

available

contrast

then

an

x

dB

stimulus

is

one

that

has

a

contrast

of

Prior

to

each

trial

the

quest

procedure

-LRB-

Watson

Pelli

-RRB-

estimated

the

performance

threshold

ct

i.e.

the

contrast

increment

required

for

accurate

first

responses

This

is

halfway

between

chance

performance

-LRB-

-RRB-

and

a

hypothetical

ceiling

of

As

a

means

of

more

accurately

estimating

the

ceiling

or

equivalently

the

frequency

of

finger

errors

a

dB

increment

was

used

on

one-ninth

of

the

trials

For

JAS

the

target

was

given

an

increment

of

either

ct

dB

or

ct

dB

with

equal

probability

on

the

remaining

trials

For

the

other

observers

target

increments

were

either

ct

dB

or

ct

This

modification

allowed

better

sampling

of

their

psychometric

functions

Finally

to

further

encourage

the

naïve

observers

to

fully

consider

their

second

responses

one

of

the

three

alternatives

to

each

of

the

obvious

-LRB-

dB

-RRB-

targets

was

fixed

at

dB

Results

Psychometric

functions

For

each

observer

and

each

pedestal

first-response

accuracies

were

fit

with

a

modified

Gaussian

distribution.In

the

preceding

expression

c

is

the

increment

-LRB-

in

dB

-RRB-

Ψ1

is

the

probability

of

a

correct

first

response

and

f

is

the

PDF

defined

in

Eq

-LRB-

-RRB-

Threshold

ct

and

σ

were

free

parameters

but

the

frequency

of

finger

errors

δ

was

not

allowed

to

vary

with

pedestal

contrast

These

psychometric

fits

were

obtained

for

purely

descriptive

purposes

Unlike

some

of

the

fits

described

below

these

were

not

driven

by

any

particular

model

of

performance

Best-fitting

values

for

δ

were

and

for

JAS

MJM

FV

MT

and

NN

respectively

When

debriefed

NN

reported

a

tendency

to

respond

before

the

end

of

a

trial

Threshold-vs

contrast

functions

-LRB-

first

response

only

-RRB-

Fig.

shows

how

threshold

varies

with

pedestal

contrast

JAS

's

and

MJM

's

thresholds

were

similar

and

formed

the

classic

dipper

shaped

function

MT

did

not

suffer

as

much

masking

That

is

his

thresholds

with

high-contrast

pedestals

were

lower

than

the

JAS

's

and

MJM

's

However

his

detection

threshold

obtained

with

pedestals

having

zero

contrast

-LRB-

or

dB

-RRB-

was

similar

between

and

dB

FV

's

thresholds

with

high-contrast

pedestals

fall

within

the

range

spanned

by

the

other

observers

thus

we

can

be

reasonably

confident

that

these

pedestals

exceeded

her

detection

threshold

as

they

did

for

the

other

observers

Second-vs

first-response-accuracy

functions

Detection

Fig.

shows

how

first

and

second-response

accuracies

co-varied

when

as

in

Swets

et

al.

's

-LRB-

-RRB-

experiment

there

was

no

pedestal

Appendix

A

contains

a

full

description

of

the

raw

data

Several

features

of

Fig.

deserve

a

detailed

description

The

axes

differ

from

those

used

by

Swets

et

al.

-LRB-

-RRB-

For

the

horizontal

axes

instead

of

signal

strength

which

may

not

be

a

linear

function

of

contrast

I

prefer

first-response

accuracy

Ψ1

For

the

vertical

axes

Swets

et

al.

used

second-response

accuracy

divided

by

the

proportion

of

first-response

errors

However

both

first

and

second-response

accuracies

are

subject

to

measurement

error

When

one

uncertain

statistic

is

divided

by

another

the

confidence

intervals

for

the

quotient

are

necessarily

very

large

To

avoid

this

problem

I

get

rid

of

the

denominator

and

plot

simply

second-response

accuracy

Ψ2

One

argument

against

this

way

of

plotting

the

results

is

that

a

large

portion

of

the

graph

will

be

wasted

because

Ψ2

Ψ1

A

dotted

line

has

been

added

to

each

graph

to

indicate

this

upper

limit

for

second-response

accuracy

Similarly

Ψ2

Ψ1

Of

course

given

a

finite

number

of

trials

we

may

find

that

the

frequency

of

correct

second

responses

exceeds

the

frequency

of

correct

first

responses

but

only

a

perverse

observer

would

have

a

greater

probability

of

being

correct

in

his

or

her

second

response

Therefore

I

have

added

another

dotted

line

to

each

graph

to

indicate

this

other

upper

limit

for

second-response

accuracy

Each

point

in

Fig.

represents

data

collected

with

a

unique

target

contrast

Several

of

these

points

reflect

only

a

few

responses

made

at

the

beginning

of

the

experiment

before

the

adaptive

staircase

had

converged

We

can

thus

have

little

confidence

in

the

likelihood

of

a

correct

first

or

second

response

with

these

targets

To

convey

this

confidence

-LRB-

or

lack

thereof

-RRB-

I

have

plotted

confidence

intervals

both

horizontally

and

vertically

about

each

point

These

intervals

are

based

on

binomial

probabilities

calculated

from

the

range

defined

by

the

limits

described

in

the

preceding

paragraph

-LRB-

see

Appendix

B

for

details

-RRB-

Modeling

finger

errors

SDT

can

be

modified

to

accommodate

finger

errors

Let

ψ1

denote

the

first-response

accuracy

without

errors

For

those

trials

containing

a

first-response

finger

error

the

probability

of

a

correct

first

response

is

-LRB-

ψ1

-RRB-

Thus

if

the

finger-error

rate

is

δ

the

overall

probability

of

a

correct

first

response

is

-LRB-

δ

-RRB-

ψ1

δ

-LRB-

ψ1

-RRB-

To

derive

the

formula

for

second-response

accuracy

it

helps

to

understand

that

first-response

finger-errors

will

be

incorrect

with

probability

-LSB-

-LRB-

ψ1

-RRB-

-RSB-

-LRB-

ψ1

-RRB-

Without

loss

of

generality

we

may

assume

that

observers

correct

some

proportion

ε

of

first-response

finger

errors

with

their

second

response

Thus

on

these

trials

the

probability

of

a

correct

second

response

is

ψ1

When

first-response

finger-errors

are

not

explicitly

corrected

I

will

assume

that

the

second

response

is

completely

random

On

these

latter

trials

the

second

response

will

be

correct

with

probability

-LSB-

-LRB-

ψ1

-RRB-

-RSB-

-LRB-

ψ1

-RRB-

Thus

on

those

trials

in

which

a

first-response

finger

error

occurred

the

second-response

accuracy

should

beSecond-response

accuracy

overall

will

be

-LRB-

δ

-RRB-

ψ2

δ

-LSB-

εψ1

-LRB-

ε

-RRB-

-LRB-

ψ1

-RRB-

-RSB-

where

ψ2

would

have

been

the

second-response

accuracy

had

there

been

no

first-response

finger

errors

To

estimate

ε

trials

containing

an

obvious

-LRB-

dB

-RRB-

increment

and

an

incorrect

first

response

were

examined

-LRB-

Because

the

highest

pedestals

had

the

potential

for

masking

even

these

large

increments

they

were

excluded

from

this

analysis

-RRB-

On

these

trials

we

may

assert

that

ψ1

and

we

can

then

solve

Eq

-LRB-

-RRB-

for

ε

Solutions

were

and

for

JAS

MJM

FV

and

MT

respectively

Maximum-likelihood

fits

These

values

of

ε

were

assumed

when

calculating

the

curves

in

Figs.

In

Fig.

the

solid

black

curves

represent

the

prediction

of

simple

SDT

that

is

when

r

in

Eq

-LRB-

-RRB-

The

dashed

lines

represent

the

prediction

of

high-threshold

theory

which

ascribes

all

errors

to

unlucky

guesses

rather

than

faint

hallucinations

-LRB-

See

Swets

et

al.

or

Solomon

for

derivations

of

these

predictions

-RRB-

Maximum-likelihood

fits

were

also

obtained

for

three

further

modifications

of

SDT

They

were

-LRB-

i

-RRB-

increasing

variance

with

power-law

transduction

-LRB-

ii

-RRB-

intrinsic

uncertainty

and

-LRB-

iii

-RRB-

low-threshold

theory

Details

of

these

three

models

can

be

found

in

Appendix

C

and

receiver-operating

characteristics

for

all

three

models

applied

to

a

yes/no-detection

task

appear

in

Nachmias

-LRB-

-RRB-

The

fits

appear

as

solid

green

blue

and

red

curves

respectively

in

Fig.

Goodness-of-fit

is

indicated

by

the

generalized

-LRB-

log

-RRB-

likelihood-ratios

in

Table

Specifically

these

values

reflect

the

maximum

log

likelihoods

minus

the

conventional

upper-bound

on

log

likelihood

described

in

Footnote

Note

that

unlike

some

generalized

likelihood-ratios

-LRB-

Mood

Graybill

Boes

-RRB-

these

can

not

be

expected

to

follow

the

chi-square

distribution

because

there

are

so

many

conditions

-LRB-

i.e.

specific

increment

contrasts

-RRB-

containing

only

one

or

two

trials

-LRB-

Wichmann

Hill

-RRB-

Only

for

JAS

low-threshold

theory

produced

by

far

the

best

fits

of

the

three

SDT

models

In

fact

the

best-fitting

low

threshold

for

JAS

was

effectively

a

high

threshold

never

exceeded

by

zero-contrast

pedestals

That

is

why

JAS

's

red

curve

in

Fig.

is

visually

indistinguishable

from

the

dashed

black

line

Since

JAS

's

results

are

consistent

with

a

high

threshold

they

are

inconsistent

with

the

findings

and

conclusions

of

Swets

et

al.

-LRB-

-RRB-

For

the

other

two

observers

the

sigma-to-mean

ratios

of

the

best-fitting

increasing-variance

models

were

between

and

similar

to

Swets

et

al.

's

-LRB-

-RRB-

estimate

of

Thus

these

results

can

be

considered

a

successful

replication

of

Swets

et

al.

's

At

the

end

of

this

section

I

speculate

on

why

JAS

's

results

differ

Transducer-independent

estimates

of

r

At

detection

threshold

as

described

above

the

raw

data

were

simply

fit

with

a

multiplicative-noise/power-law-transducer

version

of

SDT

However

with

suprathreshold

pedestals

we

can

not

be

certain

what

shape

the

transducer

takes

Increasing-variance

models

-LRB-

e.g.

Kontsevich

Chen

Tyler

-RRB-

use

a

simple

power-law

transducer

but

constant-noise

models

-LRB-

e.g.

Legge

Foley

's

-RRB-

use

a

transducer

that

is

initially

expansive

then

compressive

as

the

pedestal

increases

The

compressive

non-linearity

is

required

to

produce

masking

i.e.

threshold

elevation

from

high-contrast

pedestals

We

do

not

really

have

to

worry

about

the

form

of

transducer

because

SDT

's

predictions

for

the

relationship

between

first

and

second-response

accuracies

are

independent

of

signal

transduction

-LRB-

Solomon

Swets

et

al.

-RRB-

We

merely

need

to

quantify

how

these

predictions

change

with

the

sigma-to-mean

ratio

and

find

the

values

most

consistent

with

the

data

This

examination

of

a

transducer-independent

facet

of

contrast-discrimination

data

is

complementary

to

attempts

at

modeling

contrast-discrimination

data

without

putting

any

constraint

on

the

form

of

the

transducer

-LRB-

Katkov

Tsodyks

Sagi

Katkov

Tsodyks

Sagi

Klein

-RRB-

Transducer-independent

estimates

of

the

sigma-to-mean

ratio

r

were

obtained

by

maximizing

the

likelihood

of

observing

second-response

accuracies

given

the

first-response

accuracies

A

complete

description

of

this

process

appears

in

Appendix

D

The

best

fits

were

for

JAS

for

MJM

and

for

MT.

These

values

are

illustrated

in

Fig.

All

of

these

fits

are

comparable

to

the

maximum-likelihood

fits

described

above

Binning

accuracy

Fig.

is

less

cluttered

than

Fig.

It

has

fewer

data

points

and

no

horizontal

confidence

intervals

Nonetheless

the

same

data

appear

in

both

figures

For

legibility

I

have

decided

to

combine

data

from

increments

producing

similar

first-response

accuracies

as

determined

by

the

psychometric

functions

described

above

I

have

adopted

the

relatively

arbitrary

decision

to

use

dB

bin-widths

There

is

one

visible

consequence

of

this

manipulation

a

rightward

shift

for

one

data

point

in

JAS

's

panel

However

without

binning

the

suprathreshold

data

presented

below

would

be

impossible

to

read

I

have

also

decided

to

forgo

plotting

data

from

increments

producing

both

floor

-LRB-

i.e.

-RRB-

and

ceiling

-LRB-

i.e.

δ

see

Eq

-LRB-

-RRB-

-RRB-

accuracies

Such

data

are

worthless

at

discriminating

between

candidate

models

Finally

also

for

the

sake

of

legibility

I

have

also

decided

to

cull

data

points

representing

fewer

than

trials

Of

course

these

latter

data

are

not

completely

worthless

they

have

not

been

excluded

from

any

model

fits

A

complete

description

of

the

binned

data

appears

in

Appendix

A.

Second-vs

first-response-accuracy

functions

Suprathreshold

discrimination

Fig.

shows

how

first

and

second-response

accuracies

co-varied

for

the

four

highest

pedestals

-LRB-

The

binned

data

are

tabulated

in

Appendix

A.

-RRB-

Plotting

conventions

have

been

inherited

from

Fig.

It

should

be

apparent

that

the

second

responses

with

these

suprathreshold

pedestals

tend

to

be

more

accurate

than

the

second

responses

at

detection

threshold

Using

the

same

procedure

as

was

described

for

the

detection

data

-LRB-

above

and

in

Appendix

D

-RRB-

values

for

the

sigma-to-mean

ratio

r

were

found

that

maximized

the

likelihood

of

observing

second-response

accuracies

given

the

first-response

accuracies

The

best

fits

were

for

JAS

for

MJM

for

FV

and

for

MT.

These

values

are

illustrated

in

Fig.

These

values

of

r

are

smaller

than

those

required

to

fit

the

detection

data

FV

's

relatively

high

value

may

have

something

to

do

with

her

relatively

high

finger-error

rate

No

detection

data

from

FV

are

available

for

comparison

Pedestal-by-pedestal

estimates

of

r

appear

in

Fig.

Most

of

these

estimates

remain

near

or

below

the

value

of

selected

by

Swets

et

al.

-LRB-

-RRB-

when

neither

the

effect

of

a

low

threshold

nor

that

of

intrinsic

uncertainty

is

considered

The

results

from

JAS

are

different

best-fitting

values

of

r

start

at

and

decrease

to

as

pedestal

intensity

increases

JAS

's

small-pedestal

estimates

of

r

are

strangely

high

As

noted

above

they

are

not

incompatible

with

the

notion

that

visual

noise

never

exceeds

the

threshold

of

visibility

in

the

absence

of

a

stimulus

Previous

attempts

to

replicate

Swets

et

al.

's

-LRB-

-RRB-

results

have

also

met

with

mixed

success

Despite

their

chronological

precedence

Kincaid

and

Hamilton

's

-LRB-

-RRB-

results

have

been

described

as

both

successful

and

unsuccessful

replications

of

Swets

et

al.

's

-LRB-

Green

Swets

and

Blackwell

respectively

-RRB-

As

yet

I

have

not

been

able

to

track

down

a

copy

of

Kincaid

and

Hamilton

's

publication

One

further

attempt

to

replicate

Swets

et

al.

was

described

by

Eijkman

and

Vendrik

-LRB-

-RRB-

They

reported

that

second

responses

for

light

detection

were

greater

than

chance

in

just

one

of

three

observers

An

alternative

interpretation

for

JAS

's

high-threshold-like

performance

is

that

he

simply

ignored

sensory

information

and

selected

his

second

responses

more-or-less

randomly

This

explanation

would

be

easier

to

swallow

if

all

his

estimates

of

r

were

high

However

with

suprathreshold

pedestals

his

r

is

no

higher

than

that

of

the

other

observers

Expectation

may

have

caused

JAS

to

change

his

strategy

with

pedestal

intensity

but

I

have

no

definitive

answer

Discussion

The

most

equitable

summary

of

these

results

is

that

they

are

consistent

with

a

performance-limiting

source

of

noise

which

increases

slightly

with

suprathreshold

contrast

Best

estimates

for

the

rate

varied

from

to

I

wondered

whether

such

small

sigma-to-mean

ratios

would

be

sufficient

to

model

the

high

contrast-discrimination

thresholds

obtained

with

high-contrast

pedestals

or

whether

a

saturating

transducer

function

for

stimulus

contrast

would

also

be

necessary

Previous

attempts

-LRB-

Kontsevich

et

al.

Solomon

-RRB-

to

fit

contrast-discrimination

data

without

compressive

transduction

have

not

focused

on

the

minimum

necessary

sigma-to-mean

ratio

but

that

ratio

can

be

inferred

from

the

published

parameter

values

Fitting

contrast

discrimination

In

those

previous

attempts

the

standard

deviation

of

visual

signals

was

allowed

to

increase

as

a

decelerating

power

function

of

the

mean

Specifically

-LRB-

Kontsevich

et

al.

considered

only

suprathreshold

contrast

and

thus

could

set

σ0

Solomon

used

σ0

-RRB-

Therefore

the

sigma-to-mean

ratios

decreased

as

the

means

increased

From

the

best-fitting

parameter

values

I

have

used

a

contrast

of

to

infer

the

minimum

sigma-to-mean

ratios

required

to

explain

contrast

discrimination

without

compressive

transduction

The

smallest

of

these

ratios

was

-LRB-

obtained

using

the

parameter

values

fit

to

observer

SV

with

sustained

stimuli

in

Kontsevich

et

al.

-RRB-

Thus

it

seems

that

the

sigma-to-mean

ratios

estimated

in

the

present

study

may

in

fact

be

able

to

produce

appreciable

masking

Four

different

models

were

maximum-likelihood

fit

to

all

of

JAS

's

MJM

's

and

MT

's

data

Details

of

all

four

models

appear

in

Solomon

-LRB-

-RRB-

One

of

these

models

was

a

four-parameter

non-linear

transducer

model

with

constant

Gaussian

noise

-LRB-

i.e.

where

r

-RRB-

This

transducer

is

initially

expansive

then

compressive

as

the

input

increases

Foley

-LRB-

-RRB-

obtained

good

fits

to

contrast-discrimination

thresholds

with

this

model

but

we

already

know

this

model

will

over-estimate

second-response

accuracies

particularly

in

a

-LRB-

zero-pedestal

-RRB-

detection

experiment

-LRB-

Solomon

Swets

et

al.

-RRB-

In

the

other

three

models

that

were

fit

to

JAS

's

MJM

's

and

MT

's

data

the

variance

of

visual

signals

was

allowed

to

increase

with

the

mean

Two

of

these

models

have

already

proven

capable

of

producing

acceptable

fits

to

some

of

Foley

's

-LRB-

-RRB-

thresholds

-LRB-

see

Fig.

of

Solomon

-RRB-

In

one

of

these

a

power-law

transducer

is

responsible

for

the

dip

in

the

contrast-discrimination

function

In

the

other

intrinsic

uncertainty

produces

the

dip

The

remaining

increasing-variance

model

explored

in

this

paper

uses

a

low

threshold

to

produce

the

dip

Fit

details

appear

in

Table

Initially

four

parameters

were

allowed

to

vary

freely

in

each

fit

For

JAS

and

MJM

the

best-fitting

model

was

the

one

with

increasing

variance

model

and

intrinsic

uncertainty

In

general

the

fits

improved

as

uncertainty

M

increased

For

JAS

and

MJM

the

fits

of

the

increasing-variance/intrinsic-uncertainty

model

remained

superior

when

M

was

fixed

at

a

value

of

When

the

relationship

between

signal

mean

and

standard

deviation

was

forced

to

be

linear

-LRB-

i.e.

q

in

Eq

-LRB-

-RRB-

-RRB-

the

fits

of

the

model

remained

superior

They

even

remained

superior

when

M

was

fixed

at

a

value

of

Thus

all

of

JAS

and

MJM

's

data

can

be

satisfyingly

summarized

by

a

relatively

simple

model

combining

increasing

variance

with

intrinsic

uncertainty

Within

the

context

of

this

model

the

best-fitting

values

of

r

-LRB-

regardless

of

constraints

on

M

or

q

-RRB-

were

for

JAS

and

for

MJM

These

values

are

nearly

identical

to

the

transducer-independent

estimates

-LRB-

for

JAS

and

for

MJM

-RRB-

described

above

When

MT

's

data

were

fit

with

a

increasing-variance/intrinsic

uncertainty

model

the

best-fitting

values

for

the

sigma-to-mean

ratio

and

intrinsic

uncertainty

were

r

and

M

respectively

However

his

data

are

best-fit

by

the

constant-variance

nonlinear-transducer

model

-LRB-

Foley

-RRB-

Thus

in

two

out

of

three

cases

the

contrast-discrimination

data

can

be

satisfyingly

summarized

by

a

model

of

intrinsic

uncertainty

and

increasing

variance

Compressive

transduction

is

not

required

Sensory

thresholds

for

contrast

discrimination

Although

sensory

threshold

means

different

things

to

different

people

-LRB-

Swets

et

al.

-RRB-

it

is

usually

understood

to

be

some

sort

of

barrier

weak

stimuli

must

overcome

to

be

perceived

-LRB-

Swets

-RRB-

However

it

is

no

less

valid

to

apply

the

concept

to

the

task

of

contrast

discrimination

even

with

large

pedestals

That

is

forced-choice

errors

may

occur

simply

because

all

the

alternatives

appear

identical

and

the

observer

simply

guesses

incorrectly

Inspection

of

Fig.

should

be

sufficient

to

rule

out

any

high

sensory

threshold

for

contrast

discrimination

The

data

shown

there

are

even

less

similar

to

the

-LRB-

dashed

-RRB-

high-threshold

prediction

than

Swets

et

al.

's

-LRB-

-RRB-

detection

data

-LRB-

not

shown

-RRB-

However

some

proportion

of

correct

second

responses

may

indeed

have

been

just

lucky

guesses

which

is

to

say

my

data

can

not

rule

out

a

low

threshold

for

suprathreshold

contrast

discrimination

Other

models

The

logic

of

this

study

hinges

on

the

assumption

that

unmasked

suprathreshold

contrast

discrimination

can

be

modeled

with

a

single

sensory

mechanism

Although

this

assumption

is

popular

it

is

not

completely

uncontroversial

Before

I

describe

other

possible

models

I

should

first

stress

the

importance

of

the

word

unmasked

In

a

highly

influential

paper

Foley

-LRB-

-RRB-

argued

that

the

mechanism

responsible

for

contrast

discrimination

was

not

immune

to

the

activity

in

differently

tuned

mechanisms

By

manipulating

the

spatial

phase

orientation

and

temporal

frequency

of

masking

stimuli

Foley

and

Boynton

-LRB-

-RRB-

were

able

to

probe

the

interactions

between

mechanisms

responsible

for

contrast

discrimination

However

when

no

masks

are

present

most

models

-LRB-

including

all

of

Foley

's

-RRB-

consider

contrast

discrimination

to

be

mediated

by

a

single

mechanism

or

channel

the

one

best

tuned

to

the

target

There

are

three

notable

exceptions

Teo

and

Heeger

-LRB-

-RRB-

and

Yu

Klein

and

Levi

-LRB-

-RRB-

have

developed

models

with

greater

physiological

plausibility

in

which

individual

mechanisms

have

very

limited

dynamic

ranges

Elsewhere

-LRB-

Watson

Solomon

-RRB-

I

have

argued

this

type

of

model

is

well

approximated

by

the

more

popular

single-mechanism

model

for

contrast

discrimination

The

two

types

of

model

can

be

considered

equivalent

when

performance-limiting

noise

is

added

after

the

outputs

of

multiple

mechanisms

are

combined

The

third

exception

was

recently

proposed

by

Henning

and

Wichmann

-LRB-

-RRB-

to

account

for

their

finding

that

the

low-contrast

dip

of

threshold-vs

contrast

functions

-LRB-

e.g.

Fig.

-RRB-

disappears

in

the

presence

of

a

notched-noise

mask

This

result

suggests

the

dip

is

due

to

off-frequency

looking

That

interpretation

may

be

correct

but

I

am

obligated

to

note

their

results

are

also

consistent

with

intrinsic

uncertainty

which

would

attribute

a

less-pronounced

dip

to

uncertainty

reduction

Indeed

Blackwell

-LRB-

-RRB-

argued

that

noise

both

within

the

detector

's

pass

band

and

outside

it

could

reduce

intrinsic

uncertainty

and

facilitate

detection

She

also

provided

psychophysical

evidence

for

this

facilitation

B B O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O B O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O B O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O B O O O O O O O O B O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O B O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O B O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O B B O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B B O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O B B O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O B O O O O O O O O O O B O O O O O O O O O O O O O O O B O O B O O O O O O O O O O

contrast detection discrimination threshold uncertainty noise