2 This lecture:Gestalt organising principlesSequential grouping
3 Gestalt Principles of Organisation Gestalt psychology founded in the early 20th centuryA group of psychologists: Max Wertheimer ( ), Wolfgang Köhler ( ) and Kurt Koffka ( ) formed the Gestalt schoolGestalt theory – the perceptual whole is more than the sum of its partsPut forward a set of Gestalt grouping rules that describe which elements in an image belong together to form an object – mostly described in relation to vision
4 Gestalt Principles of Organisation These principles can also apply to hearing / auditory perceptionApplication of these principles generally results in a grouping of the parts of the input sound that come from the same source - segregating those that don’tDiscuss each of the principles separatelyImportant: These principles work together – to arrive at a correct interpretation of the input sound – no single rule will always work
5 Gestalt Principles of Organisation SimilarityGood ContinuationCommon FateClosureThe Figure-Ground phenomenon and Attention
6 SimilaritySounds are grouped into a single perceptual stream if they are similar in pitch, timbre, loudness or subjective locationDemonstration 17: Failure of crossing trajectories to cross perceptuallyFalling and rising sequence are interleaved – tones from the rising and falling sequence are alternated in time.How easy is it to hear out each of the four standardsGrouping by timbre and frequency region
8 Good Continuationchanges in frequency, intensity, location or spectrum within a single sound source tend to be smooth and continuous rather than abruptSmooth change implies a change within a single sourceAbrupt change – new stream – new sourceAsa demo 12 – Effects of connectedness on segregation
9 Good ContinuationIn this example, the tendency of a sequence of high and low tones to split into two streams is reduced when successive tones are connected by frequency glidesHear H1 (2000 Hz), L1 (614 Hz), H2 (1600 Hz), L2 (400 Hz) tonesConnecting the tones, through frequency glides, helps prevent the sequence from segregating into separate streamsContinuity helps hold auditory sequences togetherStreaming stronger in unconnected sequence
10 Common FateBased on the fact that different frequency components arising from a single sound source usually vary in a highly coherent way.Tendency to start and finish together, change in intensity and frequency togetherTwo or more frequency components in a complex sound are grouped together and perceived as part of the same source if they undergo the same kinds of changes at the same time.
11 Common fateFor example, a group of frequency components in a complex sound that are frequency modulated at the same rate can be heard out as separate group from the other componentsAsa demo 24 Role of frequency micro-modulation in voice perceptionFrequency components in speech contain small fluctuations called micromodulation.These micromodulations are in all the harmonics of a vowel, and so they move in parallel
12 Common FateHear: pure tone, pure tone + harmonics (hear pure tone continuing on), micromodulation and vibrato is added to all harmonics causing them to fuse (pure tone not heard as a separate sound)Pure tone no longer heard as a separate sound – singing voice emergesThis correlated change causes the harmonics to group into a coherent speech sound – example of common fate
13 ClosureA sound may be temporarily masked by other sounds – a masked sound may be perceived as continuing behind the masker.Demonstrated through the continuity effectAsa demo 28 – Apparent continuity – does the tone appear to continue through the noise?Asa demo 29 – Perceptual continuation of a gliding tone through a noise burst
14 Perceptual organisation of sequences of sounds Sequential grouping (integration) – connecting over time – e.g. connecting of the notes of the same instrument together to create a melody – leads to the formation of auditory streamsStream segregation / fission – hear a rapid sequence of sounds – the sounds may be perceived as a single perceptual stream or they may split into a number of perceptual streamsStreaming – to denote the processes determining whether one stream or multiple streams are heard.
15 Perceptual organisation of sequences of sounds Streaming can occur if the elements making up the sequence differ markedly in frequency, amplitude, location or spectrum.More difficult to judge the temporal order of a pair of elements when they are part of separate streams than when they are in the same stream.Asa demo 1 – Stream segregation in a cycle of six tones3 high and 3 low tones – order: H1 (2500 Hz), L1 (350 Hz), H2 (2000 Hz), L2 (430 Hz), H3 (1600 Hz), L3 (550 Hz)
16 Stream segregationWhen the sequence of tones is played slowly we clearly hear the alternation of high and low tones – a single six note melody - easy to hear the temporal order of the tonesWhen played fast we hear two streams, one high and one low – a pair of three note melodies - in this case it is more difficult to hear to order of the tonesStream segregation becomes stronger at faster tone rates – segregation affects the perceived melody
17 Stream segregationAsa demo 3 – Loss of rhythmic information as a result of stream segregationTriplets of tones separated by silences – HLH – HLH – HLH… - perception of a ‘galloping rhythm’Loss of ‘galloping rhythm’ when streaming occurs – each stream has its own separate melody and rhythmIllustrates the importance of speed and frequency separation of sounds in the formation of streams
18 Stream segregationFor perceptual segregation of a sequence of tones – played at a fast rate and large separations between the frequencies of the high and low tones.No segregation at slow speedsAt high speeds there may be depending on frequency separationAt high speeds – need large frequency separation in order for the sequence to break into two separate streams
19 Stream segregationAsa demo 5 – Segregation of a melody from interfering tones – note when you can identify the melodyAsa demo 10 – Stream segregation based on spectral peak positionHow timbre differences promote segregation
20 Stream segregationTwo tones with the same fundamental but different positions of spectral peaks (i.e. where in the frequency range is the most energy) – difference in timbreDuller tone – spectral peak at 300 HzBrighter tone – spectral peak at 2000 HzTones alternated in a galloping rhythm which gradually speeds upHear separate streams of brighter and duller tones?
21 Figure-Ground phenomenon and Attention Generally don’t attend to every aspect of the auditory input – certain parts are selected for conscious analysisComplex sound analysed into streams – we attend to one stream at a time – attended stream stands out perceptually – rest of sound becomes less salientseparation into attended and unattended streams – ‘figure-ground phenomenon’.Attend to one conversation at a time at a party – other conversations form a background
22 Figure-Ground phenomenon and Attention Possible to switch attention from one conversation / melody to another, and we may be aware of other sounds, but is seems that one stream at a time is selected for complete conscious analysisImportance of changes – the listeners’ attention is usually drawn to aspects of the sound that are changing – it becomes figure while the relatively unchanging part(s) become background
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